If you put 2 apparently identicle cars side by side and invited a roomfull of buyers, the original car would sell for more than the non-original car every time. That's a fact (jack). But by how much is the question. And there is the opportunity for fraud.

Even the most experienced and esteemed experts on early 911 values get regularly surprised by dollar numbers because value changes constantly. There is no such thing as fixed value on collectibles, but, the people that can assess trends and movements and can best-guess the market are the most effective predictors. But even then, someone with way too much money comes along and pays wa-a-ay too much for the car he always wanted and wads up everyone's panties. Hah! "Shoulda been more." "Shoulda been less." "Holy crap, he's asking HOW much??! (bastard)." Whatever it is, it's worth comment.

Engine cases are born unstamped, then assigned numbers to go into a particular chassis. Newborn cases were made available to the public to replace a broken original. The factory did it all the time in-house for customers and then stamped in the original case number. That was the intent. Hell, they even replaced entire bodies on balled up customer cars and stamped those with original numbers. There is, in fact, a factory part number for the bare replacement body or body-in-white for every model of the 911.

As Rick said, you thinking it's pure, there is likely a non-original, un-whole, bastardized, devalued, spoiled and defiled otherwise collectible 911 sitting in your garage. The horror. Sell it to me... cheap.