Retractable shoulder belts

I have a 73 duster with the 2 piece lap/shoulder seat belts and want to put in the retractable shoulder kind.

Where are the mounting holes for the belts?

I have the hole at the top just above/behind the door and the one on the floor below the door panel, but I'm guessing I would need to make a hole on the floor next to the seat for the lap belt between the seat and the door.

any pics or measurements?

Thanks