I have a passenger seat for my 51 panel. It looks exactly like the drivers seat, except it doesn't mount to the sliding tracks.
The passenger seat has two hinges mounted to brackets that attach to the the front edge of the seat platform. The back of the seat has a pieace of flat steel, approximately 1/8 thick by 1 in wide that forms a foot for the rear. It has rubber pads on it where the corners rest on the platform. It folds down and then the back of the seat lifts and pivot towards the dash.
I don't have pics at this time, as the parts are dissassembled and in prep for painting.
Also for what it's worth, the Art Deco seats were similar, but not the same.
As far as rarity goes, the seats in general are rare, but the mounts for the passenger seat is what is really rare.
