35's will fit with a level kit, but don't expect to load the bed down and you'll rub with anything over very mild off road use.
I know a few with 12.5's on 8" rims. Most tire specs call for 8.5 though. Biggest issue you'll have is getting them mounted. A buddy of mine went through hell trying to get a set of 35x12.5x17's mounted on his stock rims, even if he bought the tires from them. Two different places (tire chain centers) told him it was not only awarranty issue, but an insurance issue for them as they spec'd 8.5's. He ended up going to a small local sole proprietor tire place and got it done.