1964 Dart seat belts

So my 64 Dart 4 door has Anchor brand front seat belts and only one Anchor brand rear seat belt. As I see it, the front seat belts are in the correct factory installed holes in the floor and maybe replaced the factory originals. I will be installing my new front seat belts in the same mounting positions.
The rear seat has me a bit more confused...The one rear seat belt that is currently installed is literally bolted through a small rubber floor plug with a big washer on both sides of the rubber plug. Wow, whoever did this must have been more interested in the look and not the function of a rear seat belt.
So I found this paragraph in the owners manual that says the rear floor is marked in exact locations to drill holes for rear seat belt installation. Does anyone know the location of these holes? I have the interior completely out of the car and I don't see any places on the rear floor that look like marks for seat belt installation.
Thanks in advance for the help.
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