Our resident farriers and trimmers must be out catching up on trims during this brief period of warmth we are having. Hopefully they will come in and comment
If that is two vertical cracks (about 1 to 1-1/2 inches apart) I am seeing on the right front, I'm not buying those can't eventually be made to disappear. Unless the horse suffered a really bad laceration to the hoof or above it, that will prevent it from closing.
My 18 yo TWH lives with a ridge on his hoof from a life-threatening injury he received in his youth, before I bought him.
Here comes the standard two questions - lol
1. Details of his diet, including amounts and don't forget the hay
2. Is it possible to have someone help you get close up pictures not only of the tops of the hooves in question but the soles?
If you don't have a barn or a shed, shovel a level spot big enough to where you can put the camera on the ground and still have it level with the hooves.
Take front, sides, and directly behind the hooves so the heels can be clearly seen.
Don't wash his hooves, as wet hooves skewe the issues in pictures. You can take a stiff bristled brush and a hoof pick to them, instead
You're in Massachusetts? Lots of frozen ground and probably plenty of divets or him to walk around.
There will be folks who disagree with me, but I would put boots on him for part of the day. He can't wear boots 24/7 but, if they are good fitting trail riding boots, he can leave them on 12 hours every day. Be sure to scrub the insides every night. I have been booting my foundered horse for nearly two years and send him out on 20+ acres without issue but, the boots have to fit snug enough they won't come off and still not rub his heel bulbs.
I know I'm asking a moot question when I say "who in the sam hill would rescue a Mustang and then let the things happen to this horse that happened to him? I hear about this a lot. It's just what a wild horse needs. Many kudos to you for taking him and the very best in your future with him - he's a pretty fella