Retractable REAR seat belts in a 69 Dart Hardtop

Hello, i have a 69 Dart Hardtop (pillarless). All the interior is out. The rear parcel shelf looks like it has provision for retractable seat belts. There is a slot either side and what looks like a mounting point. Does anyone know if this was an option back in 68-69? Or have any pictures of their 68 69 Dart back seat that has rear retractables installed?

BTW, i am talking about 3 point shoulder retractable. Australia had to have the 3 point shoulder system from the start

While i am assembling the car it would be a nice touch to have these. Even if they are not factory, but are after-market ones, they will tidy up the rear seat belts. I am in Australia and the car had standard Australian (non-retractable) seat belts from factory so i am required to put them in the rear to get it passed for registration.

Thanks for any help.