engine/transom mount compatibilty

[phantomv170]

I have an 89 Mariner 100hp. I was looking at getting an older 85hp Merc. The merc has a minnkota trim unit, while mine has the mariner trim.
Are the transom mounts standard from the older 85 merc( think its a 77) . Or would it be better, if possible even, to leave my mount and trim, and put the 85 merc onto my mount?

 

[Chris1956]

The older Merc 850 would likely have a different bolt pattern than your 89 Mariner. I am not sure what the Minikota PTT unit has. Four 1/2" bolts in an upside-down trapezoid pattern is the std bolt pattern, and should be used on your Mariner.

I am not sure if the powerheads or midsections interchange on those motors, but several on this board should know.