The first heads that were legal replacements for the 65's were the "replacement heads" aka "twin plug heads" aka "Ross Foundry heads" aka "433 heads". I assume the heads made in the late 90's were also legal. They let people run all kinds of stuff in S/S now.
You only need to worry about being correct casting numbers or "legal" heads is IF you get torn down after winning a NHRA race or set a NHRA class record
NHRA tech has changed a bunch on what is legal in both Stock and super Stock
Contact your NHRA division tech department or NHRA tech national to get the straight scoop on what they allow
