tire sizes

I have a 1996 chevy cheyenne 1500 i have the chance to get a set of A/T’s 31x11.5x15 will these fit my truck i can also get 31x10.50x15 i think is what they were would the fit my truck without rubbing and would they be ok on offset rims? my truck does not have the z71 on it like the silverados thanks