Just so we do not confuse the OP too much. Short block= Block, Crank, pistons, etc. Long block= short block plus cylinder heads. Big Blocks (454, 496, 502 Chevy, 460 Ford 440 Chrysler) are really just larger dimensionally than a small block (350, Chevy, 302 Ford, 318 Chrysler). Big blocks typically create more torque, but often weigh 30% more than a small block.
Motor Boatin', if you need work on the bottom end, put in a long block, and stick with your small block 5.7 (350)
Hopefully you just need a head reworked