You might try to find a Dana 44 out of a stock '87 XJ Cherokee or MJ Comanche with the tow package, it's almost a direct bolt in, with the spring perches and shock mounts needing to be moved. It comes with larger, 10 x 2.5" drum brakes with finned drums. The track width is exactly right, too. 8.8" axles have a narrower track and the diff is offset more to the side than the Jeep axle, which can result in a driveline vibration at highway speed. The driveshaft may need to be shortened 1", depending on your lift, since the Dana 44 diff pinion gear is longer than the one on the 35 axle.

The Mopar 8.25" axle from a late model XJ with stock 29 spline shafts is plenty strong, too. Also, almost a direct bolt in, too! KJ Liberty 8.25 axle rear disc brakes will bolt to this axle (junkyard discs) if you have to have discs.

The Explorer (and KJ) rear disc brakes have very weak parking brake functioning because the effective size of the park brake drum is only around 6" diameter and the parking brake shoes are only about 1" wide. The problem comes up especially with large tires with a manual trans (no Park !).

A '94-'95 YJ dual diaphram brake booster and master (from one with the ABS system) is a great upgrade for the '91 YJ, too. Adapt the late model prop valve for more rear braking. A ZJ prop valve will work great for 4 wheel discs.