converting 60's vintage fiberform i/o to ob

I've got a 20' Fiberform. The transom is probably 2 1/2" thick. I'd like to put an OB on it. It has a 150hp OMC now. I've read some other threads and talked to some of the aluminum bracket builders. So it seems like this is done all the time. One poster (Loveofsea) suggested that reshaping the transom and adding a splashwell would be a better (less stress on the boat) approach to take. I'd like to hear? more opinions on the one approach vs the other. I'd also like some opinions on what size OB people would suggest. I don't need to break any speed records and it won't be put in the ocean. I will mainly fish and hunt out of it but would like enough power to avoid making a career out of gettin' there and back. Thanks for the help.