I am in the prossess of putting shoulder harnesses in my 71 and don't want to drill any holes in the car. The setup that i have seen and like is the 2 straps going through the 2 headrest posts and then crossing and then attaching to the factory tapped holes where the rear seat belts attached. where the straps crossed they were anchored together by a steel clip kinda like a childs car seat uses. what would be the proper anchor to screw into the rear seat holes? Any paticular type of harness that seems to be "made to fit" in these early cars?