I've had 56 and 57 sedans - the back seat bottoms had a very similar mount setup with the front having pegs like that which 'clicked' into metal sockets in the floor .... the difference being 1) the seat and back were 2 seperate pieces 2) the back of the backs were a boxboard stuff 3) the bottom-front edge had a slight rounded notch for the driveshaft hump .... thinking about it, any rear seat I can recall was 2 seperate pieces
OTOH, with those hook thingies on the rear and no adjustment possible, it just about has to be a rear seat [or custom made], I think any pickup would have either a slider track or a hinged back, coupes had both slides and hinged backs
Bill
