Or even standard coil setup.
That too is an option. The same company that I planned to use for the front long arm kit also makes a coil conversion kit for the XJ rear, which is close to the same, but the MJ wheel base is longer than the XJ. I spoke to the guys there briefly about it and they weren't too sure about doing it on an MJ as their kit shares the same control arm mounts as the front and would need really long arms for the rear unless other arrangements were made such as a separate mounting point for the rear arms. I'm certain it could be done and it could make my axle plans that much easier. Maybe.