If I may step in here & offer some sound advise! Forget the engine rail bull shiat & get the damn thing on the water! When you go into production then you can dimension the engine in the boat & fab from there... You can & will drive yourself crazy trying to please everybody with the proto type. I would assume you will have your hands plenty full just working the bugs out of the dual jets, that motor & a proper hardware set up... I would "rough" the boat out first, then drive the piss out of it. Shake down all the bugs then go back & glam it out!
... oh... and one more thing... Maxi forgot to mention that you should trick it out with dual starters.