If it's truly a numbers matching car, which most people take to mean at least the engine and transmission are original to the car, the engine and the transmission will have a partial VIN stamped on them that should match the plant & sequence number of the car's VIN plate. Where the partial VIN is stamped depends on the assembly plant. Atlanta & KC engines are normally stamped on the rough cast area by the oil filter while other plants on the the engine pad with the Tonawanda engine ID stamp

http://chevellestuff.com/1969/chevelle/engines/vin_location.htm

Engine components should also be date correct for the engine itself.

 

As the above stated. Make sure it's FACTORY stamped. Alot of forgers out there these days...