I've been into my project XJ now for a few months. Things to do if you're wanting to do 35's as I'm doing is get a good 5.5" to 6.5" suspension lift. Don't have to have long arms, but they are recomended with that height.
Dana 44 rear with a locker will hold 35's, but D30 up front is pushing it if you wheel it hard. That much pressure on the pinion and u-joints WILL go boom. 33's on a D30 with locker is max.
33's with 4.5" lift will still require trimming because you will still get into the fenders. 35's with 5.5" to 6.5" and you still have to trim.
Any XJ will do as long as the motor and tranny are good. Check those points as Brad stated also the suspension points for cracks. Pull the carpet out as soon as possible, floor pan is notorious for rusting out 'cause water gets trapped under the carpet.
Frame stiffeners are good to shore up the unibody. TnT Customs, Detour USA, and others fab some good ones or you can make your own with some 2" angle iron. These need to be plug welded.
Sorry for the bandwidth as these are only suggestions, but come after much research and mistakes and wasting money on parts I can't use. Got any questions let me know in a PM. These are only a few ideas and MUCH more info to be had by the hard core XJ guys. They are incredible rigs!
Also try
www.XJdb.com.