Yeah it was my 500 that we got the bits from, but the thing is, thats what thieving ringer scum do too.

So the only way you are going to know, is if the numbers are in the shell and you are confident they always have been, identifying the engine as correct is important to know that you have a 500 with the right bits on it, but it doesnt tell you if its a 500 or not.
If you got a 500 and swapped all the bits with a base model and ended up with a 1.6 pinto engine and no kit etc on the 500 shell, that would STILL be a 500, where as the other car (like mine) would never be one.