could someone explain the actual definition of a numbers matching car.

the date code for tne block and transmission match the year of the car itself. that's about it. for instance, a block code of c6 (1966) would probably be used in a 1966 or 67 mustang.

Depends on the manufacturer, GM puts the VIN on the block and also stamps it on an axle tube and the transmission case on some years. So if its the original block, it will have the VIN and the number stamped on the block be the same. Knowing where to look is the big thing.

Different years on Fords had different things. VINs moved around a bit over the years.. lol. You gotta know what you are working with and where everything should be. That goes for all cars really.

Some cars arent more valuable with the original engine, but the hi performance ones usually bring quite a bit more with the original block. How many people blew up the BOSS engine, or the Ram Air IV, or scattered the HEMI while racing it? That is why the big power cars are worth more with the first engine, they usually havent been beaten on as much and its all there. I only have two vehicles that it makes a difference on, but I have 4 of them with the original engine, trans etc.

Only time it really matters is if someone wants to restore the car. restomods and racers dont care and usually swap in whatever they have built for it.

If you need a Vin# translated try these sites.
I used them before purchasing my car.
They explain it better than I could.

http://www.fomoco.com/mustang-vin-decoder.shtml
http://iml.jou.ufl.edu/projects/students/Blommel/
http://www.autoinsurancetips.com/mustang_vin.htm

Did you search google matching vin #

There are no numbers matching early Mustangs. Ford just used parts that may have even been manufactured the year before. Ford also didn't keep any records, so even Marti can't tell you what you should have.