Kudos to you for trying to help him out. So many people try to "mechanically" fix problems like his, just so they can keep riding him, and then throw him out once even the "mechanical" things don't work on him anymore.
My thoroughbred didn't have any dangerous behaviors, but she also had never learned how to be a horse. She was always in a barn, never got out with other horses, never went out on trail, was only ridden in an arena, and when I got her was VERY high stress "gotta work gotta work gotta work". She had no concept of relaxing, and taking a day off. I would turn her out with my dads horse every day (he knew how to be a horse, and was a very relaxing presence for my horse to be around), and after a year or so, she really learned how to relax and breathe. I also took her out on trail rides after almost every ride, just as a cool down, brain break for her, and after she got over the whole "oh my gosh where are the arena fences" issues, she positively loved going on trail. I believe that it is what kept her sane through all my shows, and pony club, and working almost 7 days a week.
It will take time to gain his trust, and I can guarantee that for every two steps forward, he'll take a step back, and you just have to keep in mind that he's just trying to process everything, and has to step back into his "safety" zone every once in a while. He will not be fixed overnight, and you can't get impatient with him, not matter how long it takes. He will be very frustrating at times, but you got to just keep your head in the game, and keep going.
If you stick with it, I can guarantee that the reward of gaining his trust, and the things that he will end up doing for you will far outweigh the time it took to get there, all the trial and error, the banged up body parts, and headaches trying to figure him out. Keep us posted, and put up pics. I wanna see this horse lol. He sounds like he's a beautiful horse.