The good news: That aggression is a sign he's a healthy iguana. And you keep working on it, which is the right thing to do.
When you do finally get a hold of him do you quickly walk away from his cage? If their cage is still in sight they tend to remain aggressive, so as soon as you have him take him to a different room.
I found it works best at first to just let him stay on your shoulders. Let him get used to being on you and let him walk around your shoulders and arms on his own. When he gets used to that, then you can start handling him a little more, like encouraging him to climb from hand to hand or hand to arm.