there's a step by step in the tech archives on this... i plan on doing the same one of these days.

a 12.5" (that's usually a 33" tire) on an 8" wheel is no biggie although some will say you'd need a 10" wide wheel.

4.2 '87 yj, 263,000 miles, mopar mpi, 33" mud bfg, skyjacker 4", 3.73 gears, arb lockers-f and r., tom wood's 2.07 shaft conversion, tom wood's hd driveshaft, magnaflow/custom exhaust, 4wd bumper/swing-out tire carrier