There's a wealth of knowledge out there on
www.naxja.org on XJ's. Search and learn (most is fairly accurate and there's enough knowledgeable people there to point out and correct any posting inaccuracies) but most change out the 2.8 for a 3.4L Chev motor.
2.8's only came up to '86 as far as I know. The 4.0L took over for '87 and newer models.
There's some cheap XJ's with 4.0L out there available. Get an HO version ('91 and newer) if you can and go from there........
Top 10 things to watch out for
Dos
1) 4.0L
2) non-disconnect axle with 297 jointed shafts (not critical as they are numerous and bolt-in, but you'll want one).....there was one at Pick-n-Pull a week or so ago in a green '92
3) watch for 'modified' bodies.......structural integrity is at stake
4) skids are kind of nice but not necessary
5) trailer hitches are kind of nice to help save your gas tank if you're going to wheel it
Don'ts
1) ABS---just don't.......
2) D35--plan on replacing if bigger than 32" tires are in your future (8.8's or D44's are great replacements)
3) worry about the paint----the factory paint is whacked and flakes off
4) roll it over---unibodies don't seem to care for that much
5) buy it to make a 'serious' trail rig......XJ's have limitations, but they can do anything that doesn't require removal of the top and glass. If you want to do upper Helldorado and upper Proving Grounds and more extreme trails, buy something else. To run up to Pritchett {Moab '5' rating} and similar, an XJ is a great way to go.