Hi there, like everyone is saying, buy something cheep, after all you are going to have to change most of the suspension, new tires, maybe a new stroker, how knows, it is all just for fun and learning, if I had the chance I would go for a 97 or 98 with at list 150k or something around that, and do a RE long arm 3.5” to 4.5” lift with very good shocks like fox, and Deavers leaf springs on the back, go with 32” tires, and beef up the axels, install lockers on both axels, a tire to tire steering system, and from there on test it to see how it works.
Xj’s are very versatile vehicles and you can spend a lot of cash on them, they are endless toys, it all matters on what you want it for.