it's a typo, he either meant 231 or 242, only 1 number off either way. and now that I think about it, I'm near certain the MJ was never offered with a 242, only the XJ.
You could put a 231 in there as well. I like the 242 for a dd. I have 1 in my 98' Grand Cherokee that is currently down with a bad tranny. I like having 4 high part & full time modes as well as the 4 low and 2 wheel drive. I really don't use 4 high full-time much, but I do in the winter in the rain. I had a 95' Grand Cherokee previously and had the crappy np-249 t-case with the all time 4 high and didn't like it that way. It did o.k. offroad with 3" lift and 31's though. That was before I got my beastly 91' xj. Get Crash's t-case.
Troy