I just put a set of '91 1100 rims on my '86 750. No handling probs and it fits fine. I am running a 120/70ZR17 front and 180/55ZR17 rear with no clearance problems. If you have to buy the rims anyway I'd say get them from an 1100 with a 5.5" rear so you can run the 180 tire on the rear. I ahve put about 400 miles on since finishing the swap and have found no unusual handling characteristics.
You should have no trouble mounting the wheel. Before I put on custom wheels I did the same thing. The only problem you my have depends on the tire you use. It may rub on the brake stay arm. To fix just put a slight bend in it where the tire rubs.
I have the stock arm and had to do no mods to brake stay. But, as Bones said, it depends on the tire. I am running Metzeler Rennsports and I had no clearance problems. Even if you run into he tire hitting the stay it is an easy fix.