i think something like a comp cams 280 magnum hydraulic with a good dual plane intake topped with a 750 or up holley dp And at least a 9-1 comp would work out just fine.Now if you want a race motor then you need alot more.The best increase can be found in reworking the pump also.For a lake boat motor or your needs i think you will be fine with a cast piston and 2 bolt block i really wouldnt think you will be spinning past 5300 rpm.(with an A or an AB impeller assumed)