They will say the backspacing in the description if you order them online. If you are looking in person, set the back side of the wheel down on a flat surface. Measure from the flat surface to the wheel mounting surface. That would be the backspacing.
92 YJ, 4.0, 5" BDS springs, 1" booms, 1" BL, 35x12.50x15 MTZ's, Ford 8.8 with LSD, 4.10 gears. It's never done though.