The Xj came with a spring over on the back. The dana 30 that came in most Xj's was a High Pinion 30 vs the Low of the YJ and TJ, and does not have the vacum disco. The HP version is said to be stronger than a LP dana 44, ring and pinion wise. The detroits are a good unit ran one in a CJ no issues. Just can make on street driving a bit more fun, as it will bang and pop at certain times, making your think you axle just fell off the jeep. The ARB's are nice too, but as you said you have the compressor and air line to worry about. I currently run arb's front and rear. No isues to date, but I expect at some point way down the road it will need something. For both lockers the biggest part is the install. get someone who has done a lot of them. The air line install, just flex the suspension out and give some slack for the air line. Mine are on a TJ so the line is routed on top of my control arms then up to the frame.