I should have added that is down to the owner to prove age of vehicle at point of scrutineering with log book, HTP, FIA papers, etc, etc.
There is no doubt that head restraint devices are a life saver in the event of the "wrong" accident, and one should not put a price on safety, but they can be a real pain to deal with in many historic cars. They are not fitted to the cars as Frank implies, but are fitted to the driver and his helmet and held in position by the safety belts, which must be positioned correctly, and therein lies a problem. A HANS device must be fitted to suit the seat angle, unless you purchase an adjustable one, which still may not work for your particular set up.
The harness type that Simpson produce are a lot more belt than hard material and are useable at all angles, but still need the helmet restraint strapping to be adjusted for each application. For me, it was the only one that was comfortable and user friendly with my type of cars and helmet use, but very expensive. Over twice the price of a HANS item.
If any of you are going racing, or your particular event demands you have one, please, I implore you, do have a proper fitting session with the car and your helmet at an authorized dealer who can guide you. It may not just be the HANS you have to purchase, but possibly a new helmet if it does not have the restraint pick up points fitted !!!!!
Hope this helps.