Ended up cutting the splined end of an upper drive shaft to get the lower unit to mount up with out binding. There is 5/8" of the splines left and was wondering if thats enough?

ya hit tha "curious" button.. what kinda (motor, horse power) gear case is to long that ya can cut some oftha splined end off and then fit.. don't know of "ANY TYPE, BRAND, HORSE POWER that's gonna be that way....same type gear cases usually come in 5 or more inche difference in length that I know of....ie: merc V6 15, 20, 25, 30 inches..

What he said. The mercury shafts are designed to fit 15, 20, 25 and 30 inch midsections. Cutting off any part of the driveshaft to get to the next sized shorter would cut all the spline off.

I think you may have made a boo boo. If you did cut it right its still going to have to be re-splined.

My buddy has a 93 Evinrude 150 that got water in the lower unit and messed up the gears
and broke the lower shaft. We found a used lu off a 86 Evinrude 150 XP and it all matched up except for the drive shaft it was just a little bit longer. It just had about 1/4" gap between the two halfs mating up and you could tell it was the shaft so i cut a little at a time until it mated without binding.

Its all back together and running good im just worried that if something gives it may damage the splines in the crank.

most outlandish "modification" (even for tha OMC) I've ever heard of.. would be really concerned 'bout above..with only 5/8' engaged.

I wouldn't want to be a long way from the dock when it lets go.

Any boat mechanic out there with any input.

You put a 90 degree lower unit on a 60 degree engine, the cranks are totally different you should be ok,