The Ford Explorer 8.8 is the way to go for an axle swap. It's about 5/8" narrower per side than the YJ axle and has the YJ bolt pattern. Find one from a '95 or later so it'll have disc brakes and 31 spline axles. They come with 3:73 or 4:10 gears and some have limited slip.

You'll have to convert the drive shaft from the flange style to the jeep yoke. You'll also need to adapt the Ford brake lines to the jeep and adapt the e-brake.

Several different companies make kits to adapt the Explorer rearend to the Wrangler (Rubicon Express, Teraflex,M.O.R.E.) .

Check out:

www.jedi.com/obiwan/jeep/ford88.html