At 11.99, you need a minimum of a 5-point (passengers side door bar not required). Swing out door bars are legal, at least to 9.99. At 9.99, you need the full 10 point cage with window net.
The MM roll bars are only legal if you weld the shock tower braces.
Check out S&W Race Cars in PA. They make mustang specific kits in both mild and chromoly. I paid $149 for the kit and another $150 to have it welded in. Pictures are on my website.
I'd suggest getting an NHRA rule book from your local speedshop and familiarizing yourself with the rules. The rules depend on how quick you plan on going. There's plenty more that you'll need to know with clutches, bellhousings, fuel lines, harnesses, etc.
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Jeff Chambers
Trophy Stock #3
11.462 Seconds / 117.43 MPH
Chambers Racing Team