when building a cage or bar think of how the forces will transfer thru the car and bar. You want all your mounting plates to be in 2 planes. I would not want the rear of my bar mounted to the seat belt bracket it is only held in with like 10 spot welds. Just because somebody sells a bolt in bar or cage doesnt mean it is a well thought out item.
http://jalopnik.com/5390934/mustang-...over-tire-wall