Maybe this will help. I had a 330 hp Merc engine in my 27' boat. Stock, with the stock prop, it would turn 4400 at full throttle. I removed the intake and stock cam, timing set and valvetrain and replaced it with a larger cam with matching components and a roots supercharger. I made a few test runs with the stock prop purely to see what the engine would(could) endure rpm and load wise. It was turning 6100 rpm when I decided not to push it further. I was running 12 lbs of boost.
The 330hp engine uses similar components to a truck engine. Cast crank and cast flat top pistons, peanut port heads, cast iron intake w/Q-jet, and small camshaft. Most of the marine big blocks I have seen are 4 bolt main, even the low hp models.
The engine is currently being turned into a 496 with alum heads and I'm adding a Super Chiller intercooler under the blower.