SmallPP

Hi all, it has been a while since I have written. I have a 17' Formula I/O Alpha 1 originally equipped with a 4.3L V6, which I have exchanged for a mildly built late model Vortec 350 (5.7L, under 400hp, maybe about 350hp) and added switchable exhaust (automated by RPM). I am changing the outdrive ratio to 1:50, but what prop would be recommended at first? I was running 1:84 gears and 21p prop with the tired V6 and seeing 50-53mph @4800 (light boat, trim up). My target is 70, and the cam power peak is about 5200 (powder rods, should be OK?). Just looking for similar setups and results. The hull is super thin, you can push the side in almost about 1/4 inch if you use both hands. I used edelbrock RPM Air Gap and GLM aluminum exhaust manifolds (fresh water MI), so the total engine weight is same as stock V6. Thanks.