I think it sounds like ahell of an idea but I have read quite a bit around here about running diesels under loaded or too long at low RPM being bad for them. I am contemplating big HP in my Sisu 30 but in gas.
Have you done some research and contacted a few owners of 30 Sisius to ask just how fast that particular 30 foot hull can be comfortably pushed?
I contemplated bolting in a QSB 480 into a 29 H&H.
After talking to two owners and asking how fast the 29 H&Hs run "comfortably" and then sea trialing a 29 H&H with Crusader 6.0 MPI 375 power I realized any diesel hp over 380 hp was "wasted".
Most of these DE hulls run best between 16-20 knots.
FWIW, Bill D
I dont mean 480 hp big but more like 350. I think to get reasonable cruise speed and fuel efficiency in a gas engine (especially in the round bilge hull I have) I will need a little more hp that you might go with diesel to get the torque numbers up where they need to be at cruise (I am aiming at about 3000 rpm for my cruise).
Probably be a 383 but I would love to fit a big block if it was within reason space wise. I realize that it might be wasted to some extent but if it meant my engine lasted longer, worked less and used less gas plus had brass balls when needed I might go for another couple grand for the larger engine.