harness bars do nothing and are pretty dumb
my reasoning:
if used with a reclining seat, your seat has a potential to break and your head may go behind the bar causing some damage,
if used with racing seats, and you roll you will be crushed.
I suggest looking into a roll bar, the harness bars are only used to certify harnesses in some motorsports evemts.
but, i bet NRG makes one for your car, that or sparco.