Re: Force 120hp outboard 91 vs 96
Short reply: BE VERY CAREFUL!
The mounting stud pattern was not ever changed from late Chrysler until Mercury discontinued Force engines. THAT IS NOT THE PROBLEM.
Sometime after 1992 Mercury started putting Force blocks on a different midleg and used a Merc lower unit. I don't follow model numbers and I don't know exactly when. At that time, however, they changed the number of splines in the crankshaft.
SO: while the 96 block will mount on the 91 midleg, It is a good bet that the driveshaft will not mate with the crankshaft. And the Merc driveshaft is not interchangeable into the earlier lower unit.
Everything on the blocks is interchangeable, so if you wanted to transplant in an earlier crankshaft with the correct splines, you could.
