That requirement has been in place a long time, a VERY long time
As far as your neck and a crash your way better off having the head rest, especially if your rear ended, hit in the back of the car, at speeds.
I've hurt my neck four times in a row on the first four launches after installing a 8 inch race converter in my old max wedge stocker that didn't require a head rest with the stock interior back then
Same thing on my current S/P car launching off the trans brake with no throttle stop, I had to relearn to stiffen up my back and neck muscle before letting go of the tranny button
1.27 60 ft. moves your body forward fairly rapidly, I had learn to make myself push my body back into the seat all the way so my neck wouldn't flex backwards on the leave, my helmet needed to hit the headrest with my back against the seat
As far as the door bar it needs to cross your upper arm between the elbow and the shoulder with your left hand on the steering wheel, when I 'm ask to sit in the seat and put my left hand on the steering wheel I make sure my elbow is slower than my hand is and my hand is below 9:0O clock on the steering wheel
I have a window net also that is required