As everybody says, there aren't many ways to go wrong with a rear axle swap. Get big jack stands. I used the Harbor Freight 6 tons (cheap for the height) with a few planks underneath. You need to get the XJ up high, and it falls, you might not fare well. My Jeep is pretty rust free, and I still had to cut a couple of the U bolts with an angle grinder. I should have just cut them all, as it would have been faster.
If you need to swap drum brakes over from one to the other there are ways to goof that up. Take pics. Find some instructions and diagrams. At least the first time, tearing down and reassembling drum brakes is harder than changing the axle.
The axle swap itself only took two hours or so with a buddy at a pretty relaxed pace. But then I had to swap E brake cables from my '99 axle to the pair from my '96 XJ, which took some fiddling. (The 8.25 and 35 have the same length brake cables, IME, but the 96 and earlier are the same length side-to-side whereas the 97+ have one short and one long to deal with the offset lever).
You could do it by yourself, too. Leave the wheels on the axle you are taking out, then put them on the axle you are putting in. They aren't that heavy, but it is still easier to roll than to lift! If you don't get the wheels that far off the ground, it is pretty easy to leave one tire on the ground, then jack the first side into place to get the U bolts started.
Note that the E brake cable goes over the exhaust, not under! If you goof that up, you'll melt the cable and it'll seize. (I was supposed to be in Moab yesterday, and instead, I'll be there tomorrow. At least I was able to track down a new E brake cable in only a few hours!)
Have fun!
Paul