Wow...what a mess.
I haven't heard back from my buddy yet on whether or not he knows if the 86 and 80 carrier are interchangeable. I'll let you know as soon as I find anything out.
One thing you might want to do is to try and find the exact oem carrier bearings in hopes that you won't have to make any adjustments to the backlash. You know how aftermarket parts can be sometimes. I know you said you aren't setup right now to make any adjustments, but at the very least, I'd use some gear marking compound. Also be sure you preload the bearings. If the carrier bearing preload is off it'll either toast the bearings or they will be loose causing your backlash to change. With a different carrier being installed you might have to make some adjustments anyways but you may get lucky. Gear pattern should let you know or at least get you close. If not, you really only need a range dial indicator to get it setup where it needs to be. Even with a range dial indicator, your final check is with the gear marking compound. If your gear pattern is good then you should be good to go. Be sure to check the drive and coast pattern. This may be stuff you already know or have thought of but thought I'd mention it just in case. I'm nowhere near an expert on all of this. I've only setup 3-4 diffs in the past but might be able to help a little if you need it.
I was thinking....we have an Envoy with the G80 and the 3.73 ratio. I wonder if you searched for say a Truetrac for your Saab and then did the same search for our Envoy. If the part number off of the two TrueTracs match up that should mean they're interchangeable, correct?
What is the G80 out of? If you have the whole rear end you could just swap out the whole thing so you don't have to worry about making any adjustments. It shouldn't take as long either.
Good luck with it all. I'm sure you'll have it up and running in no time.