Your comments about the correction bit and training to be a reiner make perfect sense. What a shame.
You have taken on a really challenging project; however, he looks to be a pretty nice horse, so it's probably worth it.
I'm going to repeat my previous advice because I feel strongly about it - forget about showing for a while and just work on *forward* and acceptance of the bit. The problem isn't just that he thinks he shouldn't ever reach forward into the contact, it's also that he thinks he should move with a shortened stride and little engagment behind. Allowing him to move in the false frame and faking the contact is just reinforcing the wrong habits.
I'm going to assume you already have him in the mildest bit possible, I might also experiment with rollers, Mikmars, happy mouths - anything to encourage him to accept the contact. (Yes, you'll have to move back to a dressage legal bit to show him later.)
I'd also be working on *lots* of upward transitions and lengthenings in all gaits to work on that forward and ensure he's out in front of your leg. I would also get out of the ring and work in the open or on trails as much as possible to lose the association with this previous training and to encourage the freely forward.
Good luck, would love for you to post back about your progress.