I got mine from S&W Racecars www.swracecars.com . The bars is pre bent for the mustang. I think it was $169 for the 8 point bar & $80 for the swing out kit.
You can still use the rear seat if you run the cross bar level with the rear seat.
Holy smokes! All of those pics are Waaaaaaaaaay more than what I had in mind. LOL I'd still like ot be able to put my kids in the back seat! Once the motor is complete and the suspension is done, I'll just have to ensure that I stay in the 11s. lol