If you decide to proceed with replacement, make ding dang sure you know what your doing and over build rather than underbuild. A 150 hp motor is more than sufficient to get you killed painfully from a transom failure from some area you guessed at. Hate to be a doomsayers but you need to make sure it's done right.

Also, check out what west marine has to offer in guidance an materials. Got a buddy that redid a 24' walk around using a deal that he basically mixed and poured in from the top. Course, his stringers and knee braces where intact and had access to prove it.

Wannabe...