Depending on your year of XJ, the booster from a 96 may require two things:
1. a 1/4 inch spacer that goes between the booster and the firewall, to properly locate the pushrod on the booster against the pedal bracket. You may also have to swap pushrods between your old booster and the one on the '96.
2. a new matching master cylinder for a '96, as the old master may not fit against the new booster, and if it does, it may interfere with the hood when it's closed.
It will be MUCH easier if you can find a 95 or 96 in a boneyard, as trying to adapt parts on a daily driver while keeping it drivable will be tough.
I scrounged all the parts for my 92 before starting the job, and wound up using a new master, a new booster, the 1/4 inch space, but reused my old prop. valve. Bending, cutting and flaring the new hard lines took the most time.