There are five places you can find the VIN on the vehicle; 

1) Dash
Complete VIN is on the driver's side of the dashboard, as shown below. The red circle indicates where the VIN is located on the dashboard.

2) Drivers Door
The complete VIN is on a sticker inside the driver's door.

A word about the Driver's Door Decal -  Two different versions of this decal were used in the 71 Model Year. Our research indicates that the change from Style #1 to Style #2 (see this thumbnail photo: ) occurred  in October 1970 between VIN series 1F05J123000 and 1F05J140000.         

3) Under Front Fenders
The partial VIN is stamped under each of the two front fenders on top of the engine compartment sheet metal. Notice it is only part of the complete VIN. The 1971 model year (1), the assembly plant - Dearborn (F), and the consecutive unit number (149141). In this case, the 05J is missing.

4) Engine Block Serial Number 
The serial number (aka partial VIN) is stamped on the rear face of the 429 block just below the driver's side head. The first two and last six digits of the vehicle VIN (ex: 1F123456) are shown in the photos below. The first digit ("1") denotes 1971, the second digit ("F") is the Assembly Plant code. The remaining six digits are the last six of the vehicle VIN. If the vehicle was a Mustang, this six digit number starts with a "1". If it was a Cougar, it starts with a "5". Note that this serial number may be nearly impossible to see when the engine is installed in the car.

More on the Assembly Plant Code

From this serial number, specifically the second digit (the Assembly Plant code), you can determine which Vehicle Assembly Plant that the engine was originally installed into a vehicle in. This is important because the Vehicle Assembly Plant will tell you the vehicle type the engine came from and whether the engine originally came from a Mustang/Cougar or another Ford vehicle. As you can see from our example above, the second digit is an "F", so based on the table below, this engine originally came from a Mustang.

A-Atlanta
B-Oakville
D-Dallas
E-Mahwah
F-Dearborn (the only assembly plant that built the 1971 429 CJ/SCJ Mustang and Cougar)
G-Chicago
H-Lorain
J-Los Angeles
K-Kansas City
N-Norfolk
P-Twin Cities
R-San Jose
T-Metuchen
U-Louisville
W-Wayne
Y-Wixom
X-St. Thomas

5) Transmission
The partial VIN is stamped on the transmission. Like the block, the first two and last six of the VIN (ex:1F123456) are stamped on a flat pad on the top surface of the C6 transmission or on top of the rough cast top flange where the trans case meets the bellhousing of the 4 speed top loader. The VIN is usually stamped on the front rail of the trans case, but  may have been located anywhere along the front rail and not necessarily to the left hand side as seen here. 

C6 Automatic

4 Speed Top Loader

Using the complete VIN from your door sticker or dashboard, you can determine important data about how your vehicle was originally built. You can decode your tag by clicking the link to the "Classic Mustang Decoder"site below:

Classic Mustang Dataplate Decoder

Engine Decoding

Engine ID Tag

The Engine ID tag was a small metal tag placed under the bolt that held down the ignition coil. 

The sample ID tag above left can be decoded as follows using the chart at above right:

ENGINE CID = 429  
MODEL YEAR = 71  
CHANGE LEVEL = 8
YEAR OF ENGINE PRODUCTION = 1970  
MONTH OF ENGINE PRODUCTION = November
ENGINE CODE NO. = Cobra Jet

(Note: Ford did not use the letter"I"in date codes because it could be confused with the numeral"1")

The chart below indicates which engine code number goes with each vehicle, engine and transmission combination.

Engine Tag Code

Engine Block Part Number

CJ/SCJ Blocks

Correct 429 CJ/SCJ Block Casting Numbers

The red arrow above left indicates the location of the 429 CJ/SCJ engine block casting number. A closeup is shown at center of the D0VE-A and the D1VE-6015-AA at right. The 429 CJ/SCJ engines used in the 71 Mustang/Cougar had either a D0VE-A or a D1VE-6015-AA block. But here's a special note about the D1VE block part numbers - CJ/SCJ  D1VE blocks have the "D1VE-6015-AA" casting number while base blocks have only a "D1VE-AA" casting number without the -6015- in the middle. This appears to be a screw-up by the factory! D1VE-6015-AA is supposed be a CJ block (since we have seen more as CJ than non-CJ), but due to the info we have uncovered (click this thumbnail photo: ), its best to verify first if the block is a thin or thick web before deciding if it is a CJ. See the two photos below for examples of this;

429 CJ/SCJ Main Bearing Webs

In addition to the casting numbers, CJ/SCJ blocks were signified by having thicker main bearing webs than the standard 429 blocks.  Note in the photo below how the webs on the CJ/SCJ block (left) get thicker, stepping from 1” to 1.4” near the intersection of the web to the sidewall while the base 429 block webs are noticeably narrower;  

Also note that the CJ/SCJ webs are taller and machined to the same height as the oil pan rail.  By contrast, main bearing webs on the base 429 (Thunder Jet) block at right get thinner as they meet the sidewall and are not as tall as their CJ/SCJ counterparts. Instead they are as cast and end below the oil pan rail. 

Two -vs- Four Bolt Mains

Since the two or four bolt caps were added after the block was cast, the casting number WILL NOT tell you if it is a two or four bolt main block. What it WILL tell you is that the block has thick main webs, making it a CJ/SCJ block (PI too). 

(Thanks to Dan Davis for the above info and photos)

Engine Assembly Date

These photos show the location of the engine assembly date stamping. This is the date when the block was assembled into a complete engine. For the 429 engine, this code is located just below the passenger side head, on the front of the block.  The code was sequenced: year-month-day-inspector code. The example shown above (0F22A) breaks down as 1970 - June 22 - Inspector code A. 

Paper Engine Tag 

       See this link: Paper Engine Tags 

Engine Heads - CJ Part Number

The red arrow shows the location of the D0OE-R part number on the 429 CJ/SCJ head. The part number is located between the center two exhaust ports facing upwards. This is the only part number for 429 CJ/SCJ heads.

Transmission Decoding
The transmission code to ID whether you have a 4 speed or C6 is on the sticker on the driver's door.  a "6" is for 4 speed (close ratio) and a "U" indicates the C6 automatic.

Transmission ID Tag

4 Speed Top Loader ID Tag

This is the 4 speed trans ID tag located on the trans case. The 71 429 Mustang had either a RUG-AZ or RUG-AZ-1 ID code on this tag.

C6 Transmission ID Tag

The C6 Transmission ID Tag is located under one of the servo bolts as shown above. Also, note the "R" on the servo cover. This indicates the transmission has an "R" Servo which only came on CJ/SCJ Transmissions. The Identification Code for the 429 Mustang/Cougar C6 is PJC-G. At right is an actual tag from a 429 Mustang C6.

Rear Axle Decoding

Axle ID Tag

Axle Tags/Codes

(Thanks to Dan Davis for this research and photo)

Paper Axle Tag

Paper Axle Tags/Codes

The red arrow on the photo at left indicates the location of the paper axle tag. This tag is about 1 3/4" wide and was located just past the inside U bolt on the axle tube just before it increases in diameter. The tag is marked with the axle code (ex: "1982A") multiple times and is wrapped around the axle tube several times.  Below left is an original axle tag removed from a 429 SCJ with a 3.91 axle. At right is another original tag alongside a reproduction. Group member Johan Lindvall created a template for the 987A at lower right. If you print it out, size it to be 1 3/4" wide.

Decoding the Axle from the Door Tag

            1                           2                           3                         4  

Above is a selection of Door Tags. Note that the axle code is key in determining whether or not a car has a CJ or SCJ engine. The SCJ engine was invoked ONLY when someone ordered a 429 car with a 3.91 or 4.11 rear axle. Tag #1 has an "R" axle code (3.25:1) and Tag #2 has an "A" code (3.50:1), therefore, these two cars are CJs. Tag #3 has a "V" axle code (3.91:1) and Tag #4 has a "Y" axle code (4.11:1). Therefore, these two cars are SCJs.  

Buck Tags

The buck tag was a metal tag attached to the front of the radiator support - often on the passenger side.  It was used to ID the partially completed vehicle body at the assembly plant. As an example, the tag at left decodes as:

1F91J531928 - Vehicle Identification Number
65D - Body Style Code: Cougar Hardtop
21M - Scheduled Build Date: December 21
225 - Assembly Line Sequence Number
backwards 6 - Inspector Number
M - Color: Wimbledon White
1D - Interior Trim: Dark Red Vinyl Bucket Seats
AC - Air Conditioning
PB - Power Disc Brakes (required w/429CJ)
DE - Dual Exhaust

First off, is the fifth digit of the VIN a C or a J   ? That's your starting point. If anything else, it is not even an original big block car. Now that we have established that it is a 429 car, check the door tag.  If you are lucky enough to find a vehicle with an original door tag, check to make sure the VIN matches the one on the dash   which should match the one on the title!

OK, turn your attention to the the axle code.  If it is a V (3.91) or a Y (4.11) , the car is a Drag Pak car since ordering either axle ratio is what told the factory that the car was to come with the SCJ engine.

If there is no door tag, pretty much the only *sure* way to tell if it is a Drag Pak (DP) car is the Kevin Marti VIN Report  or getting the original Ford Invoice.

You can however look for some clues which can tell you if the car is worth a follow up. Remember, that any or all of these *could* have been changed over the 30 years that the car has been alive:

First, is the engine equipped with a Holley or a Rochester Quadra Jet carb ? If it's a Holley, does the fuel enter on the driver's side and is there a tube connecting the front & rear float bowls on the right ? Is there a Ford engineering number on the choke horn ? What is it (D1ZF-9510-YA for 429 SCJ 4 speed/D1ZF-9510-XA for 429 SCJ C6 auto)? If it is a Rochester carb, it is not a Drag Pak car.

Check for evidence of an emission system installation -- either there is an A.I.R. pump or there is remnants of bracketry   here the unit was bolted on top of the alternator. Yes? Probably a Drag Pak car.

Next, look at the fuel pump and the incoming fuel lines. Are there two or three fittings on the fuel pump? Three fuel lines (two for 3/8" line and one for 3/16") indicate it was originally equipped with a Quadra Jet and is not a Drag Pak car. Drag pack cars had fuel pumps without a provision for the 3/16" fuel line.  Also look at the inner fender through which the fuel line(s) run. One fuel line or hole   = maybe a Drag Pak, two lines or holes probably not.

Let's check to see if the rear axle is equipped with 31 spline axles because all Drag Pak cars came with 31 spline axles.  Remove the wheel cover, center cap or what-have-you to expose the center of the axle.  If the axle has a large concave hole on the end of each shaft , it is probably a 28 spline.  The 31 spline axle can usually be identified by the flat surface with 3 dimples on the end of each shaft * .  Be careful here though because it is rumored that Ford changed the 31 spline axle in mid-1971.  I do not know the details. (Note: 429 CJ's had either 28 or 31 spline axles)  

Still with me? OK. Now crawl under the car and look at the speedo cable as it goes into the trans.  Does it go straight in or does it screw onto a little gearbox (straight for C6 , 90 degrees for 4 speed )?  If the cable is threaded onto a gearbox, this is the speedo reducer used to allow the speedo to work properly with 4.11 or 3.91 gears.  This can also identify a Drag pak car.  Non-Drag Pak cars will have the cable going directly into the trans and held there by a bracket and bolt.

Slide back and look at the rear axle...is there a tag? If so, look at the characters in the lower left -- are they 3L91 or 4L11? If so, that's a good sign; if the tag says something else, not a Drag Pak car.  If the tag is missing, is the "pig" (aka "pumpkin" or "chunk") an N case?  This is identified by a large "N" just above the pinion . If so, the car could be a Drag Pak car.

While you are there, check the fuel tank sender and count the lines going out. As with the fuel pump, two fuel lines (one 3/8" and one 3/16")   indicate it was originally equipped with a Quadra Jet and not a Drag Pak car.  One 3/8" for SCJ .

Don't forget that *any* 429 Mustang is rare and worth keeping, IMHO!
(Thanks to Dan Davis for this information)

* Note: The three hole axel shaft rule is only to be used for small and mid size cars from 1971 and earlier.