You will need 500-600 HP a side to run 75 in a 272 or a 311.

The ONLY way to faster with less power in a Mid to late 80's 272 or 311 is to get Surface Drives.

I think OFFTHEFRONT's rig runs 78-80 with 496's with 550 a side in a 311 with bravo's

MOPOWER's 272 runs 82-85 with 540's making 640 a side in a 272

These guys are right on with the numbers, these are heavy boats not speed deamons You will find some nice 242LS around for less than 15k that would work, and extra money if something goes wrong.