Marine 273 build

Those cams don't sound big. I put a 0.422/0.444 hydraulic cam in my 1965 273, and it is termed "RV/Torquer", i.e. good for low-end torque. You can tame a big cam with Rhoads leak-down lifters, but they are "all in" by 3000 rpm, so probably not needed in a boat. The 273 excels on the high end, like 7500 rpm, but should give good power at your lower limit.

Pistons are the killer price, especially if forged, which your friend likely found when buying the Egge's. You won't find a set for $90 like a Chevy SB. Your engines likely had the HiPo Commando pistons, since came with a 4 bbl. When installing them, note that most sets have a "left" and "right" bank. Some racers would swap the banks for better performance. You can read some posts here. Either way, keep the same bank set together.