OK, I'll get on my soapbox...
Do not put a full roll cage in a car unless you wear a helmet every time you drive it. In a 240Z the door hoops or halo bar will turn a minor accident into a concussion very easily. And the specified SFI padding won't help much because that padding is designed to work with a helmet, not a bare head. Don't believe me? Take a baseball bat, wrap it in SFI padding, and have your best friend hit you in the side of the head with a 25 mph swing. In a real accident it would be like Barry Bonds taking a full swing into your head.
Make a decision now before spending money on a roll cage or bar - is this a race car or a street car. You will not be able to build a safety cage to satisfy NHRA, SCCA, and street driving requirements. It just can't be done safely.