The D-44 model has ball joints, while the D-30 uses kingpin styleknuckels. I am getting ready to swing pretty much the complete drivretrain from an E/B under my MJ (Ford 9" rear, D-44, 4.10 gears allready installed by factory, NP435, D-20 (with the lower gears in it)). I am going to be using a '93 Mustang Cobra 5.0 under the hood also. So, I would say, yeah, it is a good upgrade. Just remember that the axles are a little narrower than the XJ, and either run adapter/spacers to get the wheel pattern right, or just get wheels with the correct off-set.