Yep, Porting is different between them. Reeds are different too. Some 115s(prop rated ones) have the power ported pistons which again is a different block. Other differences will be carbs, exhaust tuners, also the throttle cam is different
In addition there are also differences between the pre 1982 90hp and the post 1981 90hP(Crank rated vs.Prop Rated). And finally, there was a 90hp made in 1965, again a totally different engine.
