Chevy & GMC Vans

I have a G80 posi unit and both 3:23 and 3:42 gears for my 92 rear axle (2 wheel drive) but have no idea how to put it together. Anyone?

I do but am not gonna type it all here. Got to Yukon Gear's website and look over the install directions. You can also do many hours of Google searches and get all sorts of info.

yeesh I wouldn't either. Don't take that the wrong way markinhh. It's just not a simple process and there's an art to it.
I rebuilt my 700R4 and redoing the differential gives me pause. There are DVDs you can get on how to rebuild them. I got one, watched it 4 or 5 times and still haven't taken the plunge. Lifted has a number of posts on the subject, search the site. Take his suggestion and do some reading. If you sit down and grit your teeth for a while...the urge might go away.

I have only done two, an 8.8 Ford (1992 Crown Vic) and a 7.625 Chevy (in my '99 AWD). I got lucky both times, and it worked with the factory shims.
On the Ford, I replaced an open carrier with a Ford Trac-Lok with new bearings on the carrier only, didn't touch the pinion. I don't remember the exact numbers, but the backlash came out just barely tighter than the original, and had a nice pattern.
On the 1999 Safari, I put all new bearings on the pinion, carrier, (and not that it matters but the axles), and used the original gears, housing, and pinion shim; carefully set the pinion preload using an inch pound wrench to check drag on the bearing, and swapped in a G80 carrier in place of the original open one, and it came out on the tight end of the spectrum but within spec. I've had no problems with it other than a few leaks ( ](*,) ) with over 40K on it so far (knock on wood, banging on head).
I agree with Dean, there is a lot of good info out there, read, read and read. I was lucky that I didn't have to shim anything, you could be also, the only way to find out is to put one together, measure the backlash, and run a pattern. Shimming the pinion is the hardest, but with used parts, it seems like if you have the shim that the factory used on that pinion, you've at least got a shot that it will work.

edit: ps, Oddly, I'm half afraid of Automatic transmissions, I've done a few pumps and valve bodies, but never a complete rebuild. They have to be CLEAN, and I work in a dirt pile most of the time.

What the rest of these guys said. It's not magic. You'll never learn if you don't try it. Keep it clean. Pay attention to the details. Ultimately you're looking for a good pattern on the ring gear.