You are correct about the bolt pattern, but an 8.8 (31 spline) is stronger than a stock XJ dana44. It is a little wider than an 8.8, might have issues clearing the gas tank. Other than that it should work alright.
Grand cherokees weren't introduced until '93, the early ones had mostly dana35 with some being dana 44's, the later ones were mostly 44's. As for the Rubi axles, Dana 44 rear, ARB lockers front and rear (although lower air pressure than standard ARB's) and a Dana 44 center section in the front with Dana 30 outers. Jeep guys will jump all over those things.
hick