31" tires on 15x7" rims

I have an extra set of 31x10.5 " Goodyear Tracker tires (not even sure if they make them anymore, Great tire though) and we just put a 4" lift on my buddy's XJ. I was wondering if the 10.5" wide tires will go on the stock 7" rims safely or should he get wider rims first?

That's great news considering the kid is pretty broke (still in high school). What about wheel spacers, he'll probably need them. Any idea of the maximum spacing that should be put on a jeep if you intend to offroad with it? i'm sure that puts strain on the axles.