The 455 as delievered, DOES have more potential than a 400, but... There are now quality "stroker" kits for the 400 block, which is both more plentiful and physically stronger than a 455 block.
Running the "12s" WILL net you a static compression ratio in the 12:1 area. WAY too high for 93. Good heads, though. Among the better D-ports. Pistons are going to be the sticking point, but not too big a one. Pontiac Dude sells very nice forgings, made to order (including dished) for a reasonable price.
E-mail me if you'ld like some 1-on-1 discussion about the potential of the Pontiac.
[email protected]
Jim