Here is the bad news.................
All Airstreams are assembled from rear to front. Meaning the bathroom went in first, then the back wall then the overheads, etc.
This is why you are having a hard time getting to the screws. I tried to ix the doors in my 76 MH but was unable to get to the mounting points either so I left it be. The door was a bit stiff, but we were able to get it to open and close. The door itself hung on a slider like a pocket door. If the door was removed from the slider then it could have been tilted out. Look for holes in the top of the track. There were screws that went through the slider/hanger into the top of the door itself. The holes if you find them would be a sign that the door was removed. Airstream did not leave holes for adjustment. This is what the trouble was with ours. The door had worked a bit loose and was hanging down too far.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato