You can't beat building a 496 for a Jet Boat. I would look for something with aftermarket crank like a Eagle or Scat. H-beam rods of either brand. Forged pistons JE, SRP, Probe. For heads a set of steel Merlins or aluminums such as Dart, Canfields, AFR or RHS. Shop around. There are deals to be had. Might find something in the Spam section.