So I got it all finished, and holy crap does it drive well. There's a vibration from the back due to the pinion angle being not quite right, but that was there before I changed the axles. A new driveshaft is definitely needed though, as the original XJ one is too long (even with 4-5" of lift). To make the XJ driveshaft work with the JK D44, I ended up getting a Driveshaft flange from a Nissan MQ Patrol as this shares the same bolt pattern and locating-bore size as the JK Front yoke flange. The JK D30 and D44 pinions have the same spline count and size, so I have just swapped the yokes around for the time being.
The Driveshaft Slip-yoke needed to be shortened by about 1", as well as the Gearbox Output Shaft, as the driveshaft was too long and was bottoming out on the back of the gearbox/transfer case. Quick cut with the grinder on the output shaft (while the engine was running and gearbox in Reverse) and popped the slip-yoke in the lathe and no more issues there! I'll be upgrading to a better driveshaft down the track, but funds didn't quite allow at the moment.
Onto the front. This was the interesting one, as there was a lot of "I hope this works..." regarding the steering and panhard setup. In the end, I had to file the locating tabs down on the JK Pitman Arm to get it to sit where I wanted on the steering box. I also had to cut about 1-1.5" out of the drag link adjusters, as the OEM JK Drag link was too long. I did get a 2nd hand Synergy drag link, but it was longer than the OEM at its shortest length, so the steering could only turn in one direction.
The panhard setup I'd ordered ended up being to suit a LHD vehicle (even though the seller was adamant otherwise) and so I had to persevere with the Wooders panhard I already had. Pushing the poly bushing out, I found that a Hilux lower front strut bush was the same size, Outer Diameter and the centre tube had the correct Inner Diameter and Length to suit the original JK Panhard Mount.
Finally, the nut for the panhard bolt had to be welded in place, as the Artec coil mounts sat over the top of the JK panhard mount. Once that was in and I was sure it couldn't break off, I re-tapped the threads to clean them up and used an M14x1.5 bolt for the panhard diff mount. I actually had to shorten the panhard rod from where it was set with the XJ D30, so it's almost the same length as a stock panhard rod now. I will get around to making a double-shear bracket for the body side; but again, that's a future-me problem.
Front diff ready to go in
Steering linkages and Panhard angles are near perfect!
The wheels don't stick out as far as I'd originally thought they would
It all went together a lot smoother than I'd thought it would. I still need to make up Handbrake cables and sort out the front driveshaft, but it runs and drives and handles quite well. I've since driven it from Sydney to Melbourne fully loaded and towing a loaded box-trailer (around 500-600kg) and it drove like a dream. No bump-steer, no death-wobbles, and I still haven't yet fitted a steering damper! The disc-brakes work great, although I have a chirp coming from somewhere. The gearing is perfect, as even fully loaded it barely shifted out of overdrive for hills and the like. Economy has even gotten better too! Managed to get from Sydney to Holbrook on a single tank while towing! (may or may not have put 78L in at Holbrook though...)
Altogether I'm extremely happy with it. Some parts were really tricky to get right, and others just sort of fell into place by sheer dumb-luck. Now to get some new flares, smaller wheels (17's) and 33's