Hey Richard and others that may be interested, I recently did some front bump stop mods myself that seem to be working ok. It's a bit of a story, but I purchased some poly extended bump stops for 97+ xj's, but when I went to install them...after tearing the suspension apart, they were too large in diameter to fit in the stock bump stop perch on my '98. Well, I didn't want to put it back together only to tear it apart again later, so I "turned" them down using my router.
They had a hole through them about 1/2" in diameter, so I slid a piece of threaded rod through the bump stop and two end blocks of wood with holes drilled in them and set this contraption on my router table. Adjusted the bit up a bit and hand rotated the bump stop over the bit till the whole bump stop had been "turned" down to match the stock bump stop diameter where it fits in the cap welded to the coil perch. I then used a different bit to cut a notch in the correct spot for the perch crimp to hold the new bump stops in place. I cut them to length, installed them and reinstalled the suspension (after replacing a lower D44 ball joint and axle shaft u-joint.) First test showed that the bump stops would simply fold over upon flex! So, after much thinking, I decided to install a 3/4" steel rod into the middle of the bump stop, extending through the top of the coil guide to keep it straight. I sunk it into the bump stop 2.25" and left about 1.25" without the rod. After a lot of messing around, I got them in and tested. Although they work ok, I think I should have inserted more rod in the bump stops because they still fold over more than I would like upon flex compression. They do hold the suspension at bay much better than when they were not supported by the internal rod though. Jeff