Donald Farr
Former Editor, Mustang Monthly
June 1, 2009
Photos By: The Mustang Monthly Archives
Every vintage Mustang's VIN is stamped in the driver's side inner fender apron, which should match the VIN on the door data plate or certification label. We've seen plenty of variations over the years. Some are not centered in the outer fender's cut-out area; others may by double-stamped almost beyond readability.

With the recent publishing of Kevin Marti's The Mustang and Cougar Tagbook, the previously mysterious buck (or build) tag, as found on many first-generation Mustangs, has taken on new meaning when it comes to matching numbers. According to Marti, these metal tags were attached to the front subframe so the Body and Paint line at the assembly plant could build the vehicle to order. Because some options required the drilling or punching of holes for installation, they were identified by codes stamped into the buck tag. For example, racing mirrors on '69 Mustangs required holes in the doors, so they were identified by either "RAC" (Dearborn), "RM" (Metuchen), or "3" (San Jose). As you can see, the codes varied by assembly plant. Also adding to the confusion is the fact that not all early Mustangs came with buck tags. For '65-'66, only Metuchen-built Mustangs have them. The other assembly plants began using them, affixing them to different spots under the hood, in late 1967 (Dearborn) and late 1969 (San Jose).

Thanks to the information in Marti's book, new importance is placed on the buck tag because the stamped VIN offers yet another matching number and the codes provide proof of many important factory options, like the GT Equipment Group, air-conditioning, and upgraded stereo radios.

Shelbys received their own VIN plate over the Ford inner fender VIN stamping. For matching numbers, a Shelby VIN must match the Ford VIN underneath, which can be verified by the records maintained by the Shelby American Automobile Club.

You can take matching numbers to the next level by matching the engine to the car. This can be difficult for '65-'67 Mustangs because, with the exception of the 289 Hi-Po, the car's VIN was not stamped into the block. It's assumed that the Hi-Po was stamped either for warranty reasons or for identity purposes because those engines were more likely to be stolen.

However, beginning in 1968, federal law mandated the stamping of VINs, or partial VINs in some instances, on engines and transmissions. On Fords, the VIN is typically found on a pad at the rear of the block, between the intake manifold and transmission bellhousing. If the stamping matches the VIN on the data plate and inner fender, then it's the original block to the car, a plus for talking points and value. However, as Mustang restorer and MCA judge Bob Perkins points out, just because an engine VIN is missing or unreadable doesn't mean the engine is not original to the car. "I've had untouched Boss 302s that didn't have VINs stamped in the motor," he tells us. "And I've had them where they're partially stamped. I've got a Boss 302 where you can read the 0 and the F, but most of the consecutive numbers are so far off the edge you can't see them."

In 1968, the federal government mandated the placement of VIN tags riveted to the lower instrument panel at the bottom the windshield to make it easier for law enforcement officers to spot stolen cars. These tags are found on the passenger side of '68 Mustangs; they were moved to the driver's side for '69 and later. On '68-'73 Mustangs, this VIN must match the VINs on the door data plate and inner fender.

Engines also came with an identification tag that provided the engine code, displacement, date of manufacture, and other pertinent information. Over the years, most tags have been discarded during engine rebuilds so it's rare to find an engine with its original tag still intact.

Other major components, like transmissions, rearends, carburetors, power steering pumps, and steering boxes were also equipped with identification tags, although the presence of the correct tag doesn't always mean that the component is original to the car. In some cases, the tag may have been transferred to a replacement part. Marti's book includes a decoding section for the tag codes.

Casting, or engineering, numbers are another way of identifying parts. Nearly every part, from the engine block to the taillight lens, has a Ford casting number. While the correct casting number on a part doesn't always prove that the part is original to the car, it does make it correct to the car.

Digging even deeper, most parts have date codes that can determine if the part could have originally been installed on the car. "If the date codes pre-date the car build within a good time frame, that's as good as you can get," says Meyers. "Sometimes it can be two to three weeks before the car was built. I've even seen three or four months. It just depends on where the stuff was stored and how they rotated inventory."