[silverc4s]

After rereading this: Here may be the real question..

Can an early S that is missing it's original powertrain ever be restored in a way that is equal to an S that has matching serial numbers?

Obviously here, the answer is no.

So then the question becomes, how different is the valuation with a correct but not original powertrain?

With a close-but-no-cigar powertrain (2.7 mag cases, 2.4 E with Webers/PMOs, etc)?

Then you can know the top number that can be "subtracted from" to get your valuation, asking price.