What kind of power range are you looking for? What is the goal for the boat? Is it a big or small block set up now? I'm assuming its BBC's if its a staggered set up. What kind of hull is it for?

With out knowing details I would build a EFI stroker BBC just for parts availability of cooling system, transmission and header availability. Way to many variables with out knowing more details. Power level and intended use is going to determine outdrive selection.