'73 Silverline Comoro Stern Jump Seats

[1stgenbird]

I have a '73 Comoro with a 165hp Mercruiser with jump seats on each side of the engine box. The top of the seats have a hook and which attach to an eye on the rear deck area which I thought was the only way of securing the seats. I had both seats out yesterday and noticed a full length piano hinge on the bottom of the seat box which was folded up into the seat bottom which is why I never noticed it before. That tells me that originally the seats may have folded forward once the hook was released but I don't see anywhere on the deck where the hinge may have attached. Not sure if the hinge screwed into the floor or some sort of bracket?
Anyone have seats with a similar attachment method that could provide info how to attach?