After my own battles with "navicular" ...I put a response in your other thread. I'm a veterinary technician and I completely disagree with everything that is said about navicular by veterinarians. Its horse manure IMO. I recommend reading this by Pete Ramey DIGGING FOR THE TRUTH ABOUT NAVI
I would start a trim based off the wild horse model and treat for thrush. Keeping this horse outdoors for lots of movement is also ideal. Instead of shoes, try hoof boots for protection and traction.
I also don't blame the horse for "going nuts" they chose to ride a horse that's obivously been in pain. Of course bute is going to help make him feel better but that's not a good long-term antiinflammatory/pain solution. Try ground white willow bark 1tbsp twice daily. It doesn't have the negative effects as bute for long term use, good to use during the transition and a little after and slowly take the horse off it by reducing the dose.