What happens on the XJ, (and I think the ZJ too), is that the internal bracing inside the framerail is only thin sheet steel, that is there to keep the frame rail from crushing together when the bolts that hold the gear to the frame rail are tightened. A fix would be to drill all the through holes large enough to install thick wall steel tubing with an ID that would accept the 7/16" diameter mounting bolts, then weld them into both sides of the frame rail, so that the bolts will be once again able to be torqued to spec without crushing the rail. YJ's and TJ's already have thick wall tubing welded in to the frame for the steering gear mount so this is not a problem in these Jeeps.

This is one company that makes a reinforcement kit, that includes sleves for the frame rails:

http://www.c-rok.com/sb.html

Click on the pics to see some typical failures!

Once the original sheet metal bracing has started to crush, it will continue to do so, much like if you dent the side of a soda can, it won't hold weight anymore.