The way it was explained to me by NHRA Tech is that if you have the equipment in the car, even if it's not required, then it has to comply with the rules for the equipment. If the car is not required to have a roll bar, but it does, the roll bar has to comply with the rules. Those rules say that the seat must be attached to the roll bar and the harness must also be attached and meet SFI 16-1 requirements.