xjmarc

Sorry OP mentioned it in the first post.

comancheman

.....the CH 8.25 from an XJ will have its spring perches closer together than the mj and top vs bottom. the xj lift springs could be choped down and the main leaf used as an aal, xj aals add bout half the lift advertised for the xj when used on an mj.

as for the op's question...

.....no, the mj springs will never work safely (do not double up shackles) under an xj using the stock unibody spring mounts

.....yes, mj springs will give 6" lift...but you would have to mount the shackles to the bumper (not the stock bumper). doing this would let you chose your lift height depending on how hi or low the shackle mount is set. there are othe concerns in doing it this way, +5" to wour wheelbase, meaning body work, pinion angle and longer driveshaft.