Then I would suggest not changing the gearing yourself..
as for the check, sometimes the gear ratio is marked on a tag that is bolted to the cover. If you dont have the tag, you will have to either pull the cover and count the teeth on each of the ring and pinions.
The other way is to jack up the rig, spin the tire one complete revolution and count how many times the yoke spins; problem with that method is that it is not very accurate, but if both front and rear counts the same, then it may be right.
The XJ set up is typically different than a YJ, but it can be done. Just check it over real good and see what if any changes you would need to make.