I can't believe anyone would put a force outboard before a yamaha. My thoughts are, That if you have to get into a powerhead that deep, Tos it!. One thing to conceder is just buy a new powerhead. If it was a 150 Yamaha, You can get a new powerhead for five grand.Next thing to concider is ,Who is doing the work. There is probly only one good guy in the Bellingham area and that is Jim's outboard repair on Mt Baker highway. As a charter opperator in Craig,AK, I am able to see what works better and what seems to have problems. For my money I use nothing else than Yamaha. The mercury opti-max is also very good. They have had a little problem with the lower unit. I think it is more the opperator than the equipment. The new Honda's 130hp 4-stroke seems to have a lower unit problem. I know of five new one's in town this summer and three have craped out so far.
Anyway, what ever you do, Make sure you get a big enough engine for the boat. The biggest mistake people make is under power. You will not even get a hundred hours on an engine if you go that route.