Rear Seats Question
 

Relatively new Skymaster owner here. I have a 1967 T337B. The aircraft has four seats and I’d like to add the 5th and 6th seats. At the rear seat area the aircraft has two rails close to the sidewalls of the fuselage but no rails in the center. It looks like the side rails have always been there and it doesn’t look like any center rails have been removed. It looks to me like the rails are for a bench seat. However, I don’t see any seats in the Cessna service and parts manuals that would fit my rails. Does anyone have any insight?