manual or auto?
the pilot bearing isn't 4wd specific, that will change (or not) depending on what trans you put in. :thumbsup:
not sure what you mean by the "4wd engine harness" but I'm pretty sure you're referring to the vacuum harness that runs off the t-case.
and as he said, the brakes must match the new axle. 2wds are different and there have been changes on the 4wd ones over the years.
now is the time for gearing upgrades. better gears were available in 2.5L rigs and (unless you have the dana 44 rear) you'll want to upgrade your dana 35 too.
now is also the time to consider the front U-joints too, as the later years of XJ (also the early 90s with ABS) has bigger ones. these axle shafts are swappable into early axles if you find an early one with better gears.
a donor rig can help with a straight swap, but no XJ came with all the goodies. for example, even later 4.0 XJs had 3.55 gears at best.