What kind of info are you looking for?
Lowering is pretty straightforward to DO....
doing it right is another matter entirely..
No personal experience and I'm sure you'll find theres NO ONE on here that has personal experience lowering an XJ. Most people on

either lift their XJ to go off road or keep it stock and running right..
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That said any minitruck site should be able to help you out.
It has a pretty basic suspension with a leaf suspended solid rear axle and a coil suspended solid front axle..
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You could try going to a spring under axle config in the rear like some trucks have but you would want to get springs from a SUA truck.. like a dakota or other..
then mount your axle like that.. it should net you about 3-4 inches of drop in the rear...
Then cut your front springs to match making sure to cut only off the bottom and cut it so it will fit in the stock groove and stop for the spring end...
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Disclaimer.... This is going to ride like ASS.. bumpy solid... the shocks are probably going to bottom out so you'll want short ones if you can find them..
I'm not sure what else will interfere but you'll end up clearancing a bunch of stuff to get the axle stuffed up against the body...
Youll want shorter bump stops or you'll be riding on them instead of the springs..
See if you can find some Ford F150 lowering springs for the front of a 70 era truck.. they have springs that fit the Cherokee stock for stock and you may be able to find lowering springs for those...
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But since you posted the most generic question in the universe I'll leave it to you to ask any further questions.