Seat Mechanism

Sounds like you are both missing the cams that actuates the levers. They are an elongated cam with a round central hub. There is a square through hole that fits over the square shaft and is held in place with a very small set screw. Best bet is to see if anyone has a used set. Next time you see another 67-69 GB at a show, peek inside and take a look. You can see them easily.