I have "86 Grand Wag 44's under my MJ. There are also some waggy 44's with an off-set rear diff, and a vacume actuated front axle D/C, you don't want those. My '86 44's are non D/C front and a centered rear diff, which i think are the best for XJ's and MJ aplications. One really nice thing about the front D44 is the ability to put lock-out hubs on for about $70. They just bolt right on in about 15 min. As mentioned above the rear Waggy 44 is narrower, so I added some 1.5" spacers to fix the width. ive got 15x10 in steel wheels with 3.75" bs. I'm runnin' 38x14.50x15 TSL SX's with no rub. Right now, flex is limited by shocks, which are Rancho 9000's. Ride is great on the road too.
I opted to do a leaf spring front conversion, instead of keeping the coils, as it is less expensive. You will hear all kinds of debates on leaves and coils. I liked the coils in my XJ, I really like the leaves on the MJ. I don't hear all the poppin' and gronin' with the leaves as I did with the coils 5 link. I am also getting some really good flex out of the YJ 4" Skyjacker leaves. I also picked up some D44 knuckles from a Chevy (wrong side drop for us) to make a complete high steer set-up. I paid $50 bucks at a U-Pull for them. I paid another $30 bucks for two u-bolt D44 yokes instead of the strap style.
There are also D44 front waggy's with the rear 20 too. The rear 20 IS much stronger than the old CJ 20's, BUT you will be limited on gear ratios. I have 5:13's, with a rear full spool, and a front lock-rite.
I'm still using the stock D-shafts too.
Another nice thing about the Waggy swap, is the fact that your still all JEEP. Those full width Ford guy's can't say that...can they?
Forgive the tire ramp, but the front driver's tire is about 42"es off of the ground. I'm also using two XJ stock shakles per side in the rear to get a little more flex. The rear of the MJ is too light to get good flex without them. I'll have some real world off-road pics soon. I still have a rear main seal to replace, and an exhaust leak. Then it's AWN!!