Airframes
Benevolens Magister
In Post #22, in the second pic, top right hand side, it looks like there is only one door, opening outward (i.e away from the cockpit), with a central handle operating latches that locate into lugs on the starboard side bulkhead. The door gives the impression of being the same width as the opening, and I suspect the bulkhead and door combination acted as the seat backs - that is, the seats were pans only, presumably to accept seat-type parachutes (?). If that's the case then the harness and back-pad of the parachute would be acting as a seat-back padding.