As far as the drive shaft length. Look at it this way. He has a 3.5" lift. That lift probably runs longer arms in the factory mounts on the body. So If you draw a line from the center of each mounting hole in the body,then pull that line down,(heres where you have to picture the jeep in side view on grid paper) as you pulll the line down it will pull the end of the line closer to the body. Or picture your arm as a link bar bar. Hold it out in front of you,then drop it. it comes back to you. The same thing happens when you lift your jeep. So when you lift your jeep most manufactures will add longer arms to push the wheel base back to where it was factory. so that being said. My piont is this. With his 3.5" liftIt probably pulled the shaft out in on a low pinion axle. So when you add the Hi pinion axle it probably took the shaft length back to where it was factory. so he should be good. I never ran into hi pinion/low pinion swaps,as every XJ i have messed with had HP axles or was getting a custom suspension and drive shafts any ways. I hope this helps..