Vintage Seat belts
 

I need help. A friend of mine had a Buick in high school, back about 1986. I don't remember the model. It was a 72 or 73, and it had 2 part seat belts. The lap belt was on a retractor just like every other OEM seat belt I have seen. But the shoulder belt was in clips up in the roof above the door on both sides. You could clip it in to the lap belts buckle and you could chose to, or not to, use it with the lap belt. My question is, during what years was that belt arrangement used and was it something used on all Buick at the time or only on certain models or trim levels?