I went through the same issue and did not see a lot of good options. The double harness for the shoulders seemed to be harder to center them even on the seat so I elected to use a Y belt. I had seen even some factory cars that go through the back wall and then anchor back to the frame. It seemed to me the connection point should be high as possible on the wall and made of steel. So I welded brackets to the frame. I have also seen brackets made to the back side of the wall with the belts bolted through the wall and brackets. The other option is to add a brace on the roll bar, which puts it at the height it should be. I decided against that becasue my bar is about 3" back and I felt that on the passenger side it would rub the paint when not in use. There are a lot of trade offs on this issue.
If you have not bought your belts yet I would suggest ones where the laps pull up and the shoulders pull down. There is not much room to pull the laps down. RCI has just about all options.
Wayne
