FWIW I had a Dana clutch type LSD installed in our '95 and I couldn't be happier. Rarely chirps a tire and I've never known it to allow a tire to slip.
Some prep had been done to it prior to my buying it. Case bolts were replaced with G8's that had been drilled for safety wire. Prior to taking it to Ruben for install I thoroughly cleaned the bolt holes, applied red Lock-tite to the bolt threads, torqued them to max torque for a plated G8 with waxed threads (figured wax's Cf was closest to that of lock-tite), and then safety wired them.
No experience with parabolic springs, not even sure what that really means - suspect its merely marketing, but have had experience with the 63" long GM rear springs in other applications. A distinctive feature of these springs is a shim between leaves at the center bolt of roughly the same size as th spring perch. This reduces the internal friction in the spring significantly as the shims are the same thickness as the plastic tip sliders creating an air gap between each leaf and its neighbors. Had to go from a 255/70 Bils 7100 valve stack to a 275/78 valve stack. I know those numbers don't seem all that different, but the difference represents the loss of 'damping' in the spring itself due to friction. I had planned to experiment with adding such shims to the OME rear springs for the Tow'd, but I've decided (after making & installing the shims) that the OME springs will lift the truck higher than I want.
A friend had Deaver build him some nice springs for his '92 CTD std cab. He was working out which Bils 7100 length to employ when baby No. 1 made a std cab impractical. If they only need bushings and haven't lost ride height then a rebuild of sorts is OK. If they've lost ride height I've yet to find a reputable spring house willing rebuild the Tow'd's rear springs.
With std leaf springs you can likely go with the std. 255/70 valving and be fine on all 4 corners. I have, with long lasting success, removed the spherical bearings from Bils 7100's and replaced them with urethane bushings. Much quieter that way.
In the remote reservoir universal application 7100's there is the "short body" option. These are 2" shorter overall than the std bodied dampers in each stroke length. These used to be ab "in the know, special order" sort of thing but they're getting better known & likely have a p/n these days. The thing that makes the short body option possible is that the non remote res dampers have the divider piston above the shaft piston. With a remote res that divider piston is moved to the reservoir, so the damper main body can be 2" shorter for the same stroke length.
No experience yet, but a friend has used Lizardskin products on his Scout 80 build. I plan to use it on the Bronc-up, even if it ends up being only the base layer under some other heat & noise insulation. In the rear of the Tow'd I have lined the rear sheet metal with first a butyl noise product off amazon followed by some self-adhesive "Frost-King" closed cell foam with a thick aluminum foil skin. It has made a big difference in the rear, need to open up the doors and line them next.
Paint under/behind the dash a light color! This is huge if you ever have to work under there for any reason. I've long used Krylon Universal Gray for areas like this.
I can see where a patch of mass loading product applied to the flats of the rocker covers could quiet things down, but most of the idle noise are the injectors. Not sure there a product rated high enough in temperature for that application. I wonder if the effort would be worthwhile. If you don't still have that sheet metal piece across the top of all of them you might find a replacement. It is my understanding that engine noise is the real reason for that part.
Never really worried about diff temps. In HD applications I use Redline gear oil and move on. Trans temp is a different story. Of course that is the only gauge not working after rebuilding the whole dash in our truck. Figuring out how best to manage the trans with the OD kill switch has made a huge difference in trans temps. Our trans will lock the converter in 2nd when the OD is turned off. This is huge for pulling steep grades (like CA168 east out of Big Pine) w/o the trans getting too warm.