Almost all tires have a spec for "recommended" rim width. Simply look at the spec for the tire and see. I doubt a 31" tire will be out of "spec" for your stock rims and even if it close it won't hurt a thing.
I don't think a 31" tire will rub on the springs. I used to run 31's on my 82 and never had a rubbing issue. If you want to check and see, get the OD of your current tires and see how much room you have between the springs and tires when turned all the way. But don't forget you only gain 2" of radius on a 4" taller diameter tire.
As far as power goes, if you don't plan on any heavy hauling you'll be fine.
89 GW, 454, 700R4, 241C, 411's with posi's, 9" rearend, 2500 stall, lifted, and lots more to do.
1999 International 4700 Crew Cab 4X4, custom step side bed
2003 Durango 4x4
1982 CJ7 4 banger
2008 MB E320 Bluetec