I had a similar issue. I not fond of attaching the seat belts to the roll bar either. I also wanted to ensure that the mounting point was as high as possible to prevent spinal compression in the event of an accident.
On mine I used a 1/4 inch steel plate that I placed on the top of the rear end chassis. I drilled holes through the chassis members and bolted the steel plate to the frame using 1/2 inch grade 8 bolts.
To the plate, I then bolted 1/4 inch angle iron which had formerly been used for earthquake plates on computer racks. I cut this into 7 inch pieces, one for each side, and drilled the holes for the connection points on the steel plate and for the seat belts. To make connection a little easier, I tapped the front holes on the plate and screwed in the bolts so that I would not have to be in two places at the same time to connect the angle irons. For me, the angle iron also serves as a cover for the top of the shock tower.
I've included the link to a picture in my gallery showing how I set everything up.
http://www.clubcobra.com/photopost/s...6&ppuser=24713
You may not be able to do the same thing but hopefully it provides some ideas.
Mike