Most people are familiar with the VIN (vehicle identification number) found inside the driver's side windshield pillar of today’s modern cars. American automobile manufacturers began stamping and casting identifying numbers on cars and their parts in the mid 1950's. The obvious purpose was to give an accurate description of the vehicle when mass production numbers were starting to climb significantly.
While today's VINs are relatively standard, there was no standard with VINs, or any other numbers, with older cars. VINs, (formally called a serial number) came in all sorts of variations, which depended on the individual manufacturer at that time.
Car parts are stamped with several numbers at the time of production to verify the essential facts about the car and also to assist in manufacturing sequence. Some cars will have a significant identification plate, listing the major part numbers against which you can check. Depending on the make and model, you may find these numbers stamped not only on the engine, transmission and rear axle, but also on the alternator/generator, carburetor, distributor, water pump and heads.
When buying or selling your classic, finding out what numbers you need to verify and where they are located on the vehicle takes a diligent “Sherlock Homes” type. It can be a bit frustrating even for the experienced classic car buyer. If in doubt, contact a professional who knows that particular model car to either check the numbers for you or assist you in finding and interpreting the numbers. Good resources for such information are the many model specific clubs; their members are usually knowledgeable about their cars and very willing to help.
Depending on whom you talk to, the definition of a “matching numbers” car may vary. A classic car purist might say that a truly original, matching numbers car will still have all the parts that it was manufactured with, including the tiniest nut and bolt. That would be very hard to find in an older car, so a more practical definition might be that all the parts will be either from the assembly line at the time of production or have been replaced with authentic NOS (new old stock) parts.
The most general use of the term “matching numbers” would mean that the engine and transmission are marked with the same sequence number as the chassis VIN number, and the rear axle/differential’s date code and casting number corresponds with the vehicle that's being checked.
When you are investigating a car’s history, make sure to clarify with the seller what part numbers are matching and what parts aren’t. Then verify for yourself or with your mechanic by including part numbers in your inspection check list prior to making an offer on the car.
Finally, why bother to check the numbers? The value on matching numbers cars and originality is increasing, and you’ll find much higher prices associated with these rarer cars. It’s one more piece to the puzzle of determining the market value of the car you’re thinking about purchasing or selling.