Ok, so this is a VERY half assed answer, but it might be enough to get the ball rolling for you.
I have completely ripped apart the back end of 1980 burban, but for different reasons. I had more pictures, but this is the only one that i seem to have kept.
Now, those are both the bottom, and the top some where. It been over a year since i ripped into mine so my memory is rather foggy.
If i remember correctly, the whole upper window channel is bolted in. Behind it, up top, are infact bolt holds for the hinges for doors. I want to say that the doors of these burbans the hinges recessed into the door, but its been even long since i looked at a burban with barn doors.
If you REALLY want barn doors, skim the junk yards and stuff for one with a good rear end. If you can get a good deal on the whole thing, bring it home and swap them out, i am almost positive there a direct swap. Make sure they are the same year to make it easier on your self, but if you have the donor truck besides your, i will bet its a direct swap