That seems like way too much backspacing. I'd say go with 3.25 to 4 inches of backspacing to get the good mix of stance and not sticking out too far. It's too bad you have the 18 inch tires as an 18 inch wheel is gonna take up a lot of the height you could have used for tire sidewall. I personally wouldn't run a wheel bigger than a 16 on a YJ, and I'm sticking with 15s myself.
Denis A. Baldwin
1991 YJ 2.5L, 1" BD MML, Ultimate 8.8, Super D30, 4.88 Gears, Detroit Lockers, 36" Super Swamper SAM-26s on Ion 171s, RE SOA w/RE1445 springs, Bilstein 5150s, 3in. BL, custom cage, Warn M8000, Double D Dash/OHC, 4Low Front Stinger Bumper, DirtWorx Rear Bumper WTC, Tube Fenders, RR OTT Steering and PAID FOR.