"Rear Sway Bar Delete" was an option on XJ's from the factory. I understand the Up-Country models didn't have rear sway bars. When I lifted my old XJ, I tossed the rear bar. I would notice a little more sway on twisty country roads at 80 kph, but nothing much. And, much improved flex without the rear sway bar.
I've thought about tossing the rear bar on my current XJ, but running a stiffer front sway bar with poly bushings, and quick disconnects. Stiff on the road, flexy on the trail.
Geoff