Agreed, I don't think you will clear with the x12s. Custom bumper is great, but what about the otherside? Front fender delete kit?
Also, I don't think the maxtrac 7" will handle 37s as easily as you think. You can barely even get away with x12s and 35s without a body lift. If you really are heart set on 38s for whatever reason, 20x10s and 38x13.50 toyos would probably be best. If you just want 15 inch wide tires, then im not sure.
Trust me on this, 38x15.50s will beat up the front end of any half ton truck. And its going to slowwww that truck down. And you will need a mile for braking.
But hey, you have to go through these steps on your own. Ive already been down this road lol.