You will HAVE to run spacers for a 12.5'' wide tire with the wheel. Guarenteed. The tire will be pushed against the rear coil, coil bucket and shock. Front will also rub alot..you can adjust the steering stop but to the amount you would have to adjust it you will sacurfice alot of turning radius.
For a good quailty wheel spacer take a look at the spidertrax website. They will run you around $200 for the set.
Sorry for the bad news about the 12.5 wide tire and your wheels. I origanlly had the gambler wheels on my jeep and liked the classic jeep look of the wheel but ended up replacing them with aftermarket wheels due to backspacing issues.
You can get away without the spacers if you keep 10.5 wide tire.