Matching numbers?

The casting number should be behind the starter.

What engine's in it? 6 or 8 cylinder ?

on my old boss302 there was a boss on the top of the block just behind the intake manifold, basically the same surface the intake sealed to... that was stamped with the last 5 digits (i think) of the VIN, so there was no question of "dates" it either matched the vin or it didn't.
I'm not sure if this is the same on the earlier models however.

Ford, at least in the 60's didn't make it a common practice to stamp VIN # on engines or transmissions. Actually to find one is quite rare--it is more common for GM to mark their engines.

Most Fords parts that do have VIN stampings are the truly special cars and engines, such as the Boss 302, 428CJ, or 289 Hipo K code engines--even then Ford didn't necessarily stamp them.

On your 64' Mustang, the best you can do is to verify that the engine installed has casted part #'s and dates that are near (and certainly not later than) the assembly date of the car. I believe that it is commonly accepted that most engine blocks, heads, intake, exhaust manifolds, etc. will probably have been cast maybe 2 months before the actual car build. It could even be as much as 4 months (or more) or closer to 1 month.

Because of this, and the fact that the Mustang was introduced at the end of 1964, most Mustang people will accept any 64' built 260 V8 as being the proper engine for your original 260 VIN'ed car.

If you have a 64.5 ( or rather an early 65 according to Ford) and it's got a 260 in it, then it's a pretty good bet that's the original engine. Unless someone replaced it in the last 40 years. Now, you SURE it's a 260 ? Could also be a 289 or a 302, same basic engine. really hard to tell one from another unless you know what to look for. The casting numbers on the block will tell you for sure and it should have a 5 bolt bellhousing ( early 289's did there as well, so the casting numbers are fool proof here)

Thanks for the info guys, I really appreciate it. I've only really "cared" about numbers matching on my boss302... good to know that info about the casting number/vin relationship.