I have been talking to engine builders and other jetboaters and they all tell me big cubic inches.
But I agree with you and tend to think that if you were to build a shorter stroke, Bigger bore, and longer rod motor similiar to prostock configuration but not necessary that extreme you would be better fitted to a higher rev motor. I think this would raise the torque curve. Of course bigger cubic inches does make torque.
I just question if big cubic inches {big stroke and Bore} will put you in the rpm band that is better for jetboats.
I think a better answer is 427 stroke 4.620 bore, 7.9 rods or as long as you can get to fit in the block, and a long duration cam with decent compression would be a perfect combination for a jetboat application. You would need a full port job on good heads to maximumize the combo. If anyone out there has the dyno on his computer I would like him to run the combo with this cam spec. Lift .714 intake and ehaust 270 degrees intake 276 degrees exhaust @.050 112 degree centerline. Or if you have already built a similiar engine combination Let us know how it worked. Just My .02
Kojac...