[blykins]

I don't think I'd anchor a safety belt to the roll bar.

When I had my Shell Valley, I ran the shoulder belts through the rear bulkhead (and used the little safety belt bezels that you can get from suppliers like the Finish Line) and then bolted them to the frame rails under the trunk floor.

There are two 2x2 (if I remember correctly) lengths of tubing that support the trunk. They sit directly under the fiberglass and you can drill through the fiberglass, completely through the tubing, and then run a bolt all the way through it. There's no way you could pull a bolt out of that tubing that way.