If your index is in the 40 range you're going to see the most improvement, by far, working on technique/mechanics.
Mental game doesn't matter much if you can't hit it solid. Also, as your technique improves, typically your "anxiety" will lessen.
To try and answer your question, I haven't read many golf mental books but one book that has helped my "perspective" in tournaments is Stillpower by Garret Kramer. If you follow him on Twitter you'll basically get the jist of his stuff.
If you wanted more of a game plan to implement swing/athletic cues on the course or better ways to practice, I'd check out this guy.
Those are awesome irons. Are they the last ones they made with the red writing on the cavities and the speed slot on the bottom? I had a spit set of those in 4-7 and then the MC in 8-PW. I wish the whole set was CB, probably would have kept them!