Correct; you will simply need to weld on new spring perches (photo below). If your using a XJ 8.25" the perches from the factory will be on top; thus if you keep is SUA (spring under axle) you won't even need to remove them, simply just weld on new perches in the correct location for the MJ leafs.
The shock mounts can be re-used with your factory mounting plates. Just remember to purchase new u-bolts as well as you should never re-use the old bolts.