Tom, you are contradicting yourself here...there ARE numbers within the VIN that are also within the engine stampings, that's how you can verify if the engine is original to the car. Unless someone has gotten into the really dishonest "restamping" thing
With GM cars, the "protect-o-plate" is a vital part of original cars documentation. I have an all original 1968 Impala convertible (see my sig) with all of it's original paperwork including sales invoice, window sticker, protect-o-plate, etc. My Dad bought it new!