There is a lot of good advice here, I like all the different suggestions and plan on keeping this thread in my favorites for when Cinny finally arrives....he's very green and I anticipate a lot of problems. But anyway...
My experience with OT horses are that they have had a lot of bits SLAMMED into their mouths etc etc...which hurts. Your horse may be identifying the bridle with pain. He sees bridle, he is GOING to be in pain...this is what goes on in their heads because this is how OT horses grew up.
Be sure that his mouth is healthy and if he hasn't recently had a dental check I would do that. I have seen a lot of horses have a lot of hidden dental problems such as sharp or broken wolf teeth (which are the first to get the slam of a bit) or other problems that cause pain with the bit and even eating.
I think I would work with this guy for a good half hour or more each day on taking the bridle on and off BUT I suggest if you possibly can get a nice flavored rubber or nylon snaffle for this work. THIS IS NOT TO RIDE IN, as most horses are out of control with them. But, if there is an accidental slam or any other issue it will not clank against and hurt the teeth as much. The goal here is to have him stop associating the bridle with pain so we want to make it hurt as little as possible on our working sessions. I think this in combination with any of the above methods and a LOT of repetition will help.
It will most likely take you months or maybe even a year to get him over this.....be patient