Hmmm, good question about the alloy heads. I thought only a FEW of the comp cars got them, not all of them? For Le Man's I believe Shelby went with a iron high riser head. I wonder which was the better head, alloy of that time or iron high riser? Of course the alloy heads had a weight advantage.
"American Muscle Car" had a show about legend vs reality where they had a shop assemble a number of old school engines using only stock parts that were available when engines were on the street. No modifications were allowed with the exception of an .060 overbore. The FE 427 was probably lucky to get half that for an overbore. Here are the results, the HEMI is particularly note worthy, rated by Chrysler at 425 horse. Uh huh, and pigs fly!
The Chevy 409/409 ..........................406 HP
The Ford 427/425 Tunnel Port..............637 HP
The Pontiac 421/421 SD......................488 HP
The Chrysler 426/425 Street Hemi.........820 HP
The Chevy 427/430 L-88......................527 HP