It's been a couple weeks since I posted in this thread, but I have been chipping away at the Mounty. The front end is all back together with the new UCAs and LBJs, freshly greased hubs, and lightly used sway bar links. I gave it a rough eyeball alignment and will take it in for a real alignment soon.
Last night I finally got around to servicing the differentials. I siphoned out a bit of fluid from the front dif and it was DARK! I suspect it had never been changed. I was only able to get maybe a pint out of it, but then I pumped almost a full quart back in. I'm guessing the difference in volume had seeped out a leaky pinion seal over the years because it's pretty crusty back there. I'll keep an eye on it and top off the gear oil as-necessary. That'll be a decent way to keep diluting the old fluid with new too haha.
The rear was a different story. I suspected it had leaked some in the past by the way the dif cover was stained, but when I cracked it open, there was only about a quart in there! It looked like newer fluid too, so I'm thinking the owner had been letting it leak down then would top it off whenever he remembered (but clearly not often enough). I'm sure those trac lok clutches are toast. Whoever sealed the cover last had the RTV bead way too far in and it didn't look like it actually sealed all the way around, so I'm sure that was the cause of the leak. The glitter in the oil tells me this dif isn't worth putting a new clutch pack in, so I kept it simple with a decent cleaning, fresh RTV, and new oil (plus the added friction modifier, even though the oil supposedly had some in it).
Once the alignment is done, I believe I will have completed all the housekeeping items and gotten the Mounty back to a healthy(ish) baseline after a couple decades of neglect. You know what that means...time to mess up a perfectly good truck and slap in a manual trans and a tuned PCM! I'm already looking forward to burnouts with the 4406M in 2WD.