I just had two NHRA officials in my shop yesterday to cert two chassis's. One is a 7.5 cert cage for my El Camino that has no back bars but we built it for 25.4 cert and is very extensive and not a great set-up for a street truck (full funny car cage around driver).
I had them look at a 6 point bar we built for a 10 second camaro. The biggest issue they had was that the rear bars need to be no lower than 5" from the top of the main hoop. So those pics of Marks bar would never pass tech here. The rules don't say what min. angle of the rears bars need to be, but there are other specs that need to be followed. Roll bars down to 10.00 don't need to be certified, but still need to pass tech inspection. Tech seems to vary widely depending on the track and event. If you install a roll bar, you will need a 5 point harness and have to attach the seat to the cross bar. The cross bar needs to be within 4" of shoulder height with the seat attached.
My recommendation is to print off some of these pics and ask your local track tech their opinion. Our make a few drawings and let the tech take a look. Most techs are cool if asking before doing. This will save you a bunch of work in the long run.
Also please think about safety. After being in a wreck on the strip and having another very close call at 140+ mph, i'd rather error on the safe side. These are heavy trucks. We over built Max'd Outs cage using 2" and more bars/gussets then required and i still don't think that it is safe enough at the speeds it obtains. Although i'm getting old, lol.
Seriously, i've been racing all kinds of vehicles for a long time and have see some bad stuff happen. I've also seen people walk away from some ugly crashes when their safety equipment is done well. That is my .02 from an old safety conscience guy.
