Yes, factory seat. Thanks for the info. I'll keep looking.Bill I can't say who makes them but there is a kit to do shoulder belts/seat belts for old cars.
I remember this was a post on A Bodies and I think the 3rd point mounted to the floor or the rear door panel frame.
I am guessing you are using factory seats ?
thanks. I'll check it out.https://www.seatbeltsolutions.com/3-point-conversion-kits
These may work for you.