I had a 1986 Yam 150 and the shift rod snapped on me. I replaced it myself and yes the powerhead had to come off. It's not as bad as it sounds, I just separated and tagged all the wiring and parts that were to stay on the powerhead, and used a come along attached to the ceiling rafters in my garage to lift it off. I took me a couple of days working after work each day. It was a few years ago and I don't remember all the details, but I do remember that it was not as hard as I thought it would be. If you're able to change your oil, replace a starter or even rotate your tires, you should be able to get this done with a good manual.
Leo