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OR, HOW TO TELL A NOVA 396 FROM A DUMP TRUCK 366...
You've seen and heard it before: "Numbers matching". Usually there's a hefty price tag associated with those numbers as well. A true "numbers-matching" muscle car is always worth more than one with unoriginal drivetrain parts, so the question is, how do you determine what is and is not matching numbers? It's really not that difficult, you simply need to know where to look and how to read what you find.

In a nutshell, matching numbers refers to the various codes and dates found on all the major driveline components. These include the engine, transmission and rear-axle assembly. The engine components themselves (block, heads and intake) will have various casting numbers, date codes, and an engine identification code, all of which are important and should be correct if the car is to be considered numbers matching. In the next few paragraphs, we're going to tell you where to find the various codes that matter for the engine.

WHAT ARE THEY?
But first, let's give you a little background on why the numbers are there. The date code and casting numbers are mainly for identification and quality-control purposes. Through the casting date, the day/night shift indicator and, on some components, the "clock" position, it's possible for Chevrolet to pinpoint within an hour or so when a specific component was cast. Casting numbers also identify specific "families" of components.
For example, cylinder heads with the same casting numbers will have similar applications, although some of the finishing details, like valve sizes, may vary. Date codes are found on the block, heads and intake manifold (along with many other areas and components throughout the car, but for the purposes of our discussion here, we're not concerned with those). Casting numbers are also found on the block, heads, and intake manifold. Again, other components carry casting numbers, some within the engine itself, but we're concerned only with those that can be seen without major disassembly.

Another important set of numbers is the engine plant code/engine ID number. These were stamped on the engine at the assembly plant (the engine assembly plant, not the car assembly plant), and identified the date of assembly, which particular displacement/horsepower combination the assembly is and what chassis it was to be installed in. Additionally, after the engine was earmarked for installation into a specific car, an engine V.I.N. was stamped into the block by the final assembly plant. The number included a division identifier (1 = Chevrolet), the last digit of the year model, a code for the final assembly plant and the last six digits of the chassis serial number (the sequence number). The engine V.I.N. was included mainly as a theft deterrent (it's a means of linking a particular engine to a car in the case of theft). These numbers may not be found on early (pre-'65) engines.
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