JYRUS, You will run into several problems including the different bolt patterns, which drive different axles, which mean different rear wheels. Now you have different patterns and wheels front to rear. Also the backing plate bolt pattern is probably different than what your YJ has. Probably easier and cheaper to buy the kit for the YJ. Another option is to swap to the Ford Explorer 8.8" from a '96 or newer. Already has the rear disc and is a simple swap. Also much stronger than the D35.
All the above assumes you have the stock D35 still. If not, disregard and accept my apology.
'91 YJ, 4.0L 5sp, Atlas II, RE SOA + 2"BDS, 35" Explorer Xterrains, ARB's & 4.56 gears, WARN 9000i