150 Yamaha Trim Motor Replacement

[gofish]

The trim motor on my old school (~1985) 150 Yammie is pretty much shot. The up switch on my binnacle somehow got stuck in the up position after parking the boat and I didn't realize it for a couple of hours. Burned it up pretty good. It works ok trimming up until it hits that higher gear and then just spins its wheels.

Anyways, I was wondering what all goes into replacing the motor. Does the whole powerhead, etc. have to come off or can you do it without major removal of parts?
Also, any ideas where I can order a rebuilt one for a good price?

Thanks in advance for any advice.