Here are some things I toyed with last night. The two holes near the seat belt bracket are in fact threaded. The are in front of the side panel and I expect that only carpet covers them. If all cars have this I think it might be the right height for a harness bar. (Anyone have a measurement off the floor to a harness bar?)
I stuck some bolts in the holes so they would be easier to see.
The first picture shows the triangle it would make if these bars were in this arrangement. The second is a mockup I made in a few minutes from some PVC pipe. Note the lower connection to the seat belt anchor. (This is made from a piece of pipe sliced open and bent out into the shape. The lower sill has a radius that matches about the outside diameter on this 1-1/2" PVC pipe. This attempt was to see if it would work and to arrive at the angle that the pipe leans back. Pipe cut on miter saw and heated with the torch to bend.
