4.5" lift, extra bumpstops, SYE/driveshaft, a dremel or cut off wheel, 4.56s, atleast a rear locker, new wheels, if you have a 8.25 rear your fine if its a d35 you'll want a stronger rear axle.
What year XJ do you have? if its a 97+ goahead and plan on an SYE and new rear driveshaft. If you have a 231 (no fulltime option) go HD from PORC or AA, if 242 (fulltime option) just get an RE hack n tap SYE.
I'm sure next you'll ask which lift? Answer for me is RE, I've had Rustys and now RE.
How do you tell what rear axle you have? look at it from a distance (not the cover, put the entire chunk on the axle) if its rounded its a d35, if its flat at the very bottom its a 8.25. Or if you have ABS its a d35.
brand of gears? Superior or spicer for me.
Tires? I like Trxus, MTZs or even KMs for a DD.
What rear locker? depends on the $$ you got....I'd save for a detriot though.
I have a very very very hard time believing you can't find info on this subject.