Hello Rich,
This may help.
When I installed mine, I recall the manufacturer was specific that the shoulder belt should
NOT be lower than 4" below your shoulder. With that in mind, I mounted the belts with 7/16" bolts through the back wall. They bolt to a 4 x 4" steel plate on the other side. I was told this should be ample.
The brackets that come with the belts were bent slightly outwards so they would not touch the body.
