This kit is a great one for the price you pay for it. I have one on an 88'. They wheel well and the ride is nice. I however personally think that the shocks that it comes with are a little soft for wheelin. But that is my personal preference. and i think that the kit may have changed since i bought it. It may now come with adjustable shocks. I would also tell you to spend the etra dough and get the kit with the full rar spring packs. If you use the add-a-leaf deal it will wear on the main leaf and will sag prematurely.
Some things to look out for on an xj when lifting it are these. One the front eye bolt of the leaf springs. The nut is welded to the inside of a little bracket that is also welded to the frame. It is very common on the olderish XJs to break that nut off the inside of that bracket and that adds a day or two of compication to your lift project. I highly advise you to buy 2 or 3 bottles of wd40 and go to town on everything, a week or two in advance of doing your lift. It isn't too hard to get some wd40 in to the threads on that nut, if you look on the bottom of the frame rail there is a whole near where the bolt goes through, if you put your finger up in there you can feel a whole right behind the bolt and you should be able to feel the end of the bolt too. just use the little red hose that comes with the wd40 and snake it up in there and spray it real good. That will hlep everything go way smoother. Also the two upper shock bolts on the rear shocks. It is so common on every xj for those to rust and just break when you try to remove them. Get the wd40 on those for sure really good early.
If you haven't already bought an XJ look for one that doesn't have a Chrco rearend. they are not nearly as good as the dana ones (even though the dana 35 is a nothing to brag about). If you get an xj that is older than 96 then you should be ok with the drive shaft issue, But xj newer than that have problems with driveshaft vibes if you even add an inch to them.
HTH
Jerm S.