I think the rotors and maybe the calipers are different, but as long as you use the entire XJ setup, you should be just fine.
EDIT: Depending on the year of the XJ the TJ shafts should have beefier Ujoints (297's vs. 260's) but the TJ shafts should slide right onto the XJ hubs.
EDIT: Depending on the year of the XJ the TJ shafts should have beefier Ujoints (297's vs. 260's) but the TJ shafts should slide right onto the XJ hubs.