My advice to you is find a local chassis builder. Find somebody you can trust and who has done other GN's.
Have them build you a custom rollbar/rollcage out of chromemoly tubing. A 5 point rollbar is legal to 10.00. And if done properly, it can be updated with a halo to a full 8 to 12 point cage if you decide to go faster.
I've found that the generic kits offered by S&W, Alston, and others don't fit as nice as a well built custom bar/cage. Going with mild steel really adds alot of weight. CM steel is much lighter and very strong.
Build it once, do it to NHRA or IHRA specs, and enjoy the car!!
Dave