Good ideas!If you already have an SBC than you can have a decent stroker built for less than $3k. Then all you need is to install an aftermarket EFI kit $2-$3k & you would be well below the cost of the Mercury. It would be more work than throwing a crate motor in, but then you could tune the injection to your boat as well as a more highly modified engine, this would give you better economy and power.
I'm in the process of putting a 383 into my Landcruiser that is adapted to TBI (just fired it up last night). It should make about 450ftlbs at 2500rpms and 350hp at 5Krpms. Strokers make great low end, especially when using the longer 6" rods. A motor like that would be great in a heavy skipjack & be close to 200lbs lighter than a BBC.