Take off one of your stock wheels and measure the backspacing with a ruler or tape measure. That will give you the factory backspacing distance. I, too, asked the question on here about the 7 or 8 inch wide wheel for the 31x10.5 tire... lots of seasoned Jeepers use the 7 inch wheel with few, if any, problems.
If you want to mount 33x10.5's you will need a lift kit of some sort to avoid destroying the 33's... a body lift kit will be the least expensive route, but definately don't go beyond 3 inches of lift there. Some Jeepers don't suggest any more than 1 inch body lift due to additional stresses put on the sheetmetal and other components beyond the 1 inch mark.
Welcome to the Z!
