seat belt mounting

Front seat belts became mandatory during the '64 model year, shoulder belts came in sometime in '68. The mount for the receiver should be along the side of the transmission tunnel just behind the seats.

The retractor is an inertia reel. If you pull the belt out fast, it has no way of knowing if you're in a hurry or a crash. It just knows the belt is trying to go out fast and locks up.