Thanks Fred for the comment and compliment.
When we started building this car (a long, long time ago), I was planning on my 16 year old son having some driving privileges with it when completed. I wanted something between him and the outside world in case something went wrong. While at that time, I was not a seat belt wearer, I wasn't concerning myself with the mounting of them.
After enough harassment by my wife, I began to use belts and now I don't feel comfortable without them.
However, in the ensuing years and having read the arguments about belt mounting that appear periodically on the different websites, I'm still not sure about my opinion on how they should be done.
The first thing that concerns me is the idea that so many people have about the body coming off of the frame in the event of a crash. Obviously it happens as witnessed by the recent accident in Washington. But the body was basically intact which leads me to believe that the attachment on the body to the frame was minimal at best. The engine and transmission were still in place according to the photo. They are held in position by rubber mounts that would be subject to a shear load and the mass would be somewhat like that of the body and a passenger. Why didn't they come out also?
My first thought was that the body was probably mounted using the Well-Nuts that Total promotes. While your research showed them to have a tensile strength that you felt comfortable with, I believe that the shear load would be a more appropriate measure of suitability for this application.
I'm leaning to the idea that if the body is mounted solidly to the floor and the mounting bolts are sufficiently sized (1/2" is what I've got) and washers or some form of fitting to spread the load so that bolts will not pull through the floor material, it doesn't matter whether the belts are attached to the body or the frame. The belt attachment should be given the same care in deciding the method of doing it as is given to the body/frame connection.
Those are just my thoughts on it. Sorry for the rambling!
That peanut motor will give this old man all of the excitement that he can stand. You ever hear of a guy by the name of Don Cain? He used to drive the Pusch & Cain Fuel Funny car. He had the sister to this car with a bone stock 2300 Ford in it. He gave many a guy white knuckle rides in it. 1385 lbs. makes even peanut motors fun.