Livid

Have a look at what rolfhat did with the 3 cylinder 850cc block.

I gave loads of bits to beamish ken on here. Forget upgrading the 40 to a 50 it will be faster but try find a 50 g which runs the 850cc power head or find a 60 or a 70. Boat will take the power no problem as long as you have the transom supports. Your problem will be finding insurance