The earlier XJs had a longer tail shaft housing that helped prevent vibes, not sure of the years. You may be able to get by with a t-case drop, every Jeep is different though. I had vibes from 15 to 40 after I installed my lift, a week later I installed the SYE and moved the front drive shaft to the rear, and then picked up another for the front at a salvage yard. Like tanyj said, it's the best way to go.