rear seatbelts

Did they ever offer rear sholder belts. Im installing a set of rear sholder seatbelts out of a late 80's GM and much to my suprise there is already holes in the rear dash in the correct locations. A small modification to the bracket and one hole drilled and the belts fit just like ma mopar knew that 45 years later someone would do this. Btw this is in my 67 Dart. Thanks. pics to be added later.