My 70 Cutlass S has both a non-retractable shoulder belt and a retractable lap belt. The Shoulder belt is larger and fits the only buckle in the bench seat. The lap belt is the same shape but smaller and has no mating buckle to attach to. It is not the notch type I have seen elsewhere that fits into the shoulder buckle. I have two questions.
1) I have not been able to find a mate for the lap belt. Anyone know where I can get one or do I have to replace it with a set of both the belt and buckle?
2) I see 3 point harnesses but assume this requires drilling a hole for the upper attachment and possibly replacing the retractable lap belt below. How do I get the existing shoulder belt off the car in order to install one of these?

 

your lap belt is the smaller male end, look on ebay and you can find single replacements for the male end. You sure its not stuck behind the front seat on the floor. Maybe someone on here will have an extra small female end. You should have three of those for the front seat. Two retractables on the outside of the seat - one for driver and one for passenger. Then you would have one non-retractable male ended seat belt for the middle passenger in the front bench as well. WIth all three having a female end.

 

Have you looked in between the seat back and bottom cushions to see if it got pushed in there? In fact, have you looked at the anchor point on the floor behind the seat. There should be belts bolted to the floor on either side of the driveshaft tunnel. Each of these anchor points should have THREE belts held with one bolt - half of the belt for the center passenger, half of the outboard lap belt, and half of the shoulder belt.

The belts were there when the car left the factory.

Also, just to be clear, you are aware that the "retractable" lap belts aren't inertia reel, right? You need to pull them completely out of the holder and adjust how they fit with the female end of the belt. The "retractor" is for storage only, not load carrying in a crash.

 

That explains why I always grab the wrong female buckle when I go to drive. I didn't realize the shoulder belt was a different size( I'm always learning something new about these old cars)