Build the roll bar high enough so the 5-point harness doesn't hold you sitting nice and upright while the roof collapses onto your head. Do you plan on wearing a helmet, also? Doing race stuff on a street vehicle doesn't make good nonsense.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!