Outer Limits 4x4 Board

did two inch lift on my xj last week and was wondering about the gearbox spacer kit the came with it.... looks like it has something to do with the transfercase crossmember but not sure of why i need it and where exactly to put it any help would be tops

This is for your gearbox/trans crossmember goes between them to drop it down you should use it help with pinion angle as you have a fixed yoke output