Don't do either. Dont invest a lot in a D30, and the Rubi D44 isn't much of an upgrade, not worth the expense to swap in.
They way people justify their decisions is interesting, but consider the following.
Everyone touts the high pinion reverse cut gears engaged on the driver side as if that was enough to make the D30 a better axle. 4.56 gears in a D30 gives you a tiny pinion with only 9 teeth on it, mated with a 7.2" ring gear with 41 teeth. Hold them in your had and turn the pinion in the ring gear and you will see how little engagement you really have. I don't care if its coast side, drive side, east side or whatever, you've got very little contact area engaged, 4.88s are even worse. A low pinion 44 has more contact even if it is on the coast side.
You can truss the D30, and throw bank a vault door on it as a diff cover, but nothing you do will change the size and strength of the carrier, ring&pinion, bearings etc. And there is no way to prvent the deflection that pulls the pinion away from the ring gear. You might be able to beef up a D30 to rival a D44, but at what cost? and then what? A D44 can be built to rival stock D60.
The dana 44 housing is larger and stronger in every dimension. Thicker tubes, stiffer housing, more ribs, bigger carrier bearings, larger pinion bearing, way better wheel bearing configuration, bigger and better balljoints, manual locking hubs, etc. The only part in the D44 that is the same size is the axle shaft ujoints, but that is a good argument to go with a D60, it is not a good aruguement to go with a D30, and there are several good aftermarket ujoints available.
Also, all D44s are not created equal. A Ford 3/4 ton D44 is stronger and stiffer than a D44 from a Waggy or Scout. The cost to install any front D44 in an XJ is pretty much equally expensive. As such, there is no reason to start with an inferior housing. Even if the better Ford HP D44 housing costs you a couple hundred more at the JY, it is well worth it as it will only be small fraction of the total cost. High steer is easier and cheaper to implement on a D44 because it can be done with stock flattop knuckles, on a D30? If you go with junkyard HP D44 get the matching rear and solve your width and lug pattern issues at the same time. BTW, D60 rears can be had for $100 all day long.
As I see it you have only 3 options that really make sense:
Custom built axle from Currie, Dynatrack, Foothill, Solid etc. - expensive but bolt on with a warrantee.
HP D44 from a late 70s Ford. (78-79 F250 being best in my opinion) - cheaper but the most work, lots of options.
Or buy a set of JK D44 axles and cut and replace the brackets. - $1400 each, high pinion, selectable locker, warrantee, 65" wide. Not a bad deal at all. Although I've read about issues with tubes cracking.
If you can't do one of these, just run your stock D30 and fix whatever breaks.
Read a bunch of build threads, ask questions, plan the whole thing out, don't forget to plan a solution for with lug patterns, track width, brakes, and steering.
