hi mate firstly i think the motor should do ok in a boat,one thing i would change is the carb.If you can get a walbro wa167 to fit it will really make it come alive,you can keep it with a can muffler for a while and maybe go to a tuned pipe later if you wish.As for a boat id build the gas mono 48" not the offshore one,any bigger than 48" and the weedy just wont cut it power wise
.leave it air cooled and run it open hatch,heres my version of the 48" woody,send me your email and ill send you the plans unless you allready have them?.