Sounds like the door that sends air either through evaporator core OR sends air down to floor heat ducts. That door can't be removed unless one breaks the welds and separates the rod from the door. When I rebuilt my '69 I had to glue the new foam on each side of that door with door stuck in the housing.
If its like my '69 no one is going to remove that door without breaking welds between door and rod. Best bet is to find another housing that still has that door intact. Or fab up rectangular door, fab up rod, and weld 2 together inside housing.