the liberty 8.8 is very common in yards and a bit wider than stock so as to better accommodate the MJ's wide butt.
if you want to run 37s on a 3" lift, why not just get a 3" lift? an SOA is never going to be 3" unless the leafs are a negative arch.
you're going to need a patch from an XJ if it goes forward of the replacement parts. at some point you might be better off buying used rockers from a clean truck and seeing if they can cut more for the front bit.
for a 4.0L you need to let the axle droop as much as possible. you might even need to pop off the track bar or sway links to get that extra last couple inches. be careful that the oil pump and pickup tube are in there and can get bumped during removal if you force it to hard.