Well, I am going to disagree completely. I have dealt with literally dozens of head-shy horses. Some from abuse, but more from having people back off and do the wrong thing at the wrong time. They taught the horse by babying it and then backing away whenever it threw a head-slinging fit that it was supposed to keep its head away from them.
So, instead of babying him and being quiet and nearly motionless around him, you need to flap your hands and arms all around it until it accepts it.
This is how I do it. I start out 4 or 5 feet away right in front of the horse. I wave an arm around wildly while holding the lead-rope with the other. I expect the horse to want to get away. I do not let the horse turn around or bolt or go forward in any way, but let him go backward freely without trying to stop him. I jerk him around any time he does not want to face me and let him have slack in the rope when he is facing me and standing or going backwards. I am convinced that I can walk forward flapping my arm better and faster than he can step backwards.
Now, here is the part that makes it work: The instant he stops backing up, I stop and step back one or two steps. Then, I start toward him again, still waving and flapping my arm. When he stops again, (usually more quickly), I stop and back up again. I keep doing this and finally, he will stop backing up and will stop slinging his head. He will have figured out that if he stops, I stop and he lives to tell about it. He gets relief from doing the right thing instead of getting relief by making the person back away.
This is the first step to getting a horse over being head-shy. By day 2, I am flipping a light-weight rope over his neck, and waving my hand within 6 inches of his eye -- on both sides of his face. It is the same thing each time. You up the pressure and advance. You retreat when he accepts the pressure by standing quietly.
This works on every horse including those that have been severely injured in the past. It takes anywhere from one to three sessions with someone like myself. It takes longer if you do not have the feel and timing to back-off at the exact time you should.
I can promise you this --- I it 1000X better than trying to baby one into accepting things around and on its head.
For bridling -- do the same thing.
Leave a halter on and advance with the bridle. Let the horse back away and just keep following it. When it stops, you stop and back up. Just keep advancing with the lead in your left hand and the bridle in your right. Only leave the 'back door' open for the horse to back up.
In one session, any horse that has been desensitized to let you wave your arm and pet his face, will let you bridle him after a few advance and retreat maneuvers.
Once you conquer this concept, there is literally nothing within reason that you cannot get a horse to do!