Grinding, whirring, and "put"ting

I've got a 1989 b2600i 4x4 manual and I stopped driving it a few weeks ago because I was hearing a whirring sound (soft grinding) towards the back of the rig. A friend suggested maybe U-joints or gear oil replacement. So I started to replace the oil in the transfer case first and while I was under the truck, I noticed one of the nuts was missing that holds the drive shaft in place and the drive shaft was hanging at an angle off the other mounted flange. I was able to push it back into place and replace the nut and washer. I went to turn on the truck and now it sounds like it's misfiring on one cylinder. Some suggested a stuck lifter and that it might fix itself by driving it around. So I started the truck up again this morning to go to work, and as I was backing up, I hear another sound coming from what I think is the drive shaft. It sounds like it's laboring hard to turn and I can hear every rotation. Any suggestions on any of these three items?

HELP! Novice at repair work here but willing to get in and get dirty. I'll just need some clear information/instructions or at least a good idea of what to tell the guy I want to work on it for me.

Put it in neutral and see how much play it has when you twist the drive shaft, get a torch and have a look at the UJ.
Does it vibrate?
Check the oil level/quality in your Diff too

Check all your suspension mounts/components too while you're there
And check your transmission mount.
Sorry champ, it's a long list back there but they're all quite easy to get at

This is nuts. Do not under any circumstances, take a flaming volatile liquid soaked rag on a stick, anywhere near your gas tank. Use a flashlight for fark's sake.

Otherwise, advice is spot on.

^^^ lol, that's gold.

We only have standardlights and torches down here.
Not like you flash harry LA types

While I do know what you foreigners mean by torch, (many, perhaps most Yanks don't) I've no idea what "standardlights" are.

lol, I hope you're pulling my leg.
STANDARD_lights instead of FLASH_lights.
It's ok, it's still Tuesday over there, you'll get it tomorrow

Standard lights are what you turn on when you walk into a dark room!

Thanks for the advice. Next time I get a chance to get under my truck I'll check the drive shaft mobility. If it can move freely, than what direction do I go?

You also mentioned the U-Joint. How do I "look at that"? What am I looking for exactly. It's there. I mean it hasn't fallen out or anything but I don't know what kind of condition it's in unless I take it out.

I was planning on just changing out the oil in the front and rear diffs just as a regular maintenance deal. I have no idea when the last time that was done.

The vehicle doesn't really seem to vibrate anymore than normal. I only back the truck up a few feet and decided that it didn't sound "healthy" and pulled it back in to the drive way and took another rig to work.

FYI - I'm well versed in the lingo. I've got my British Drivers License and know my boot from my bonnet and can properly spell "tyre" when called upon to do so. Torches are on hand. Cheers.

My center U-joint, started making grindy noises, then on/off throttle clunks. Play was easy to feel, using the previously mentioned test. Visual inspection, can be tricky under the truck. When I got it out in the daylight, it was obviously ruined. Needle bearings gone. I had a photo, but I can't find it.

Two of our three U-joints are not meant to be replaceable. It can be done, but it ain't easy. I'm running a JY driveshaft. I'll take my original shaft to a good drive shaft specialist eventually.