Where there is a will there is a way.
Only permanent modifications to the car would be 24-36 3/8" holes drilled through the floor. Want to sell it? Unbolt cage, remove it. Press in $5 worth of plastic caps and put a coating of seam sealant over them. When was the last time you lifted the carpet on a car you bought to see if it had a cage in it at some point???
Here you all go, save yourself the $ for a NHRA membership, here are the rules for a roll BAR. Please note the 6" BEHIND drivers head for the main bar… on the street if you wack your head on that, your seat is broken or you are gumby.
Like i have been saying, there is always a way to accomplish what you need to do.