Used CJ Pony unit. I would go with the JC Whitney unit now. Its a lot cheaper and I think the same unit.
You locate the shoulder harnes upper anchor at the hole that is behind the headliner. Its just in front of the metal roof trim piece. You can get the backing plate at various Mustang part suppliers. The rest of the seatbelt will use the current holes that are in the car. The JC Whintney unit , I swear, is the unit I got from Pony.
I welded the upper sholder harnes backing plate into the car when the headliner was off. You can pop rivet the unit in place. It is installed behind the frame section. You would partaily remove the headliner and slip the backing plate behind the frame. Then drill the holes and pop rivet it in. YOu will cut a hole in the headliner for the anchor bolt. The lower bolts are straight forward/
If your car is apart, interior wise, then I would definately weld it in.
I just got my Andover belts in the mail yesterday. One month after ordering.
I'm going to try to install them in the next few days. I have to come up with some anchor plates for the shoulder fittings. I was thinking of some 16 gauge steel with nuts welded to the back side properly sized to slide up into the roof rail..
Lets talk about this pop riveting... I presume that you mean that you placed the anchor panel behind the roof rail metal. Thus it had to slide in from the back. In this case, the pop rivets do nothing except to held the backing plate in place until the anchor bolt is installed and tightened. Pop rivieting with the anchor exposed on the surface ofthe roof rail would not be very strong.
I'm really just clarifying this so that others don't do something stupid.
The article is good. As I said you can pop rivet them. The plate that we got is larger than the hole. It was about 2 inches by 3 inches with a integrated nut. You can easily make this if you have a welder.
A correction to my post We got the seatbelts from Pony-Concept cars. Not cj Pony. Sorry.
As I said the backing plate is positioned behind the frame section. The bolt goes through the hole that is already pre-drilled in the frame. The bolt goint through the hole in the frame and tightened into the backing plate actually holds the assembly together, I liked the idea that it was welded!
I can't remember where I found the seatbelt supplies for sale. the backing plates are available. But I can't remember where. If I find it I'll let you know. If you have the equipment. I would make it.