There is no diff between MJ and XJ clusters. Clusters from 87 - 90 are inter-changeable from MJ to XJ; the same for 91 and 92.
For 87-90, there were three types: 1) No tach, w/ large gas gauge on left side and idiot lights, 2) No tach, w/ gas gauge, and gauges for temp, amp, and oil (3/4 gauge set), and 3) a full cluster, w/tach and gauges.