Man that 4:1 would be awesome. I dont believe I would like it unless i could switch between a higher low gear and the 4:1 though. The 2.73 gearing gets annoying when your out on the trail and it flattens out into a road, then goes back into rocks, then back into road.....well, you get the idea.
Anyway, Ive been in some situations where a lower gear would off been really nice to help crawl over the rock and not give it so much gas..
The 231 should be the same x-case used in the xj's. like tjkj said, new driveshafts would be needed.

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LOST KJ'S
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Current Jeep: 2004 Jeep Liberty
-Atlantic Blue
-Air Ride Rear Suspension ; OME/Rustys Lift ; Powertrax Locker ; Moog Lower Ball-Joints ; 245/70/16 Yokohama Geolander A/T-S's on MOABS ; Flowmaster 50 SUV
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http://www.cardomain.com/id/jeepjeepster