Meaning of "numbrs matching" opinions please

[69hurstSC]

this is not as complicated as it seems. #'s matching (IMO)is simply the drivetrain (engine, trans, rearend) that the particular vehicle rolled off the assembly line with. if you grenaded the motor and replaced it with a factory correct replacement block, you no longer have matching #'s. heads, water pumps, bumpers, mirrors, to me this is all accecptable to replace.
restamping = NON #'s matching
there are a few particular grey areas that must be discussed. lets take a 69 Yenko Novas for example. these cars were born as SS 396 cars and of course those were pulled for 427's. is this still a #'s matching car? another example would be the 69 Hurst Olds. they were converted to 455's. what is everyones opinion of a car that is still dealership new, but converted somehow before the 1st original buyer purchases that car?