After some minor but inconvenient problems with my rear axle case I decided to find a Discovery I unit and swap it in. My 90 had already been converted to rear discs. I was able to get a complete rear end for $250- case, shafts, diff, hubs and top link, all pre-road salt in WA. The process is straightforward enough that pictures aren't really justified, but I though I'd share a couple of notes on the experience.
1. I broke all the tough bolts loose before putting the truck up on stands.
2. Have an angle grinder on hand. The only way the bolts on the bottom link were coming off was to cut them off. Thankfully they're easy to get to.
3. The top link ball joint was pretty stubborn. I tried the driving/braking in reverse trick to no avail. If you use heat be careful not to fry the rubber boot on the ball joint. I did use heat and the thing finally broke loose while I was just gently tapping on it as it cooled.
4. Don't panic when you go to reattach the drive shaft and it looks like your new diff is a different pattern- that thing is rectangular, not square
5. My donor axle has speed sensors. I cut the wires off leaving the sensors in place- I'm still not sure that's the best solution- comments/thoughts??
6. I stripped my old axle down figuring shafts, hubs and diff would all be good spares to have. I also now have a pair of Disco I rear springs and an anti-roll bar from the donor if anyone is interested.
7. Oh yeah- I left my brake calipers attached to the brake lines and hung them from the chassis so I never had to bleed the brakes.
Here's a pic of one end of my old axle case- for those who are sensitive to graphic depictions of rust and corrosion, please do not click on the thumbnail.