Depends. I've got 2 Mbuna with 2 new world. They don't get on but the the frontosa is about 6 inches and the biggest new world is about 5 inches. They HATE each other so I'm selling the frontosa. What type have you got?
Bad idea. I don't see how you can feed both properly, and once that texas is grown he will try to go after the mbuna (yum), unless the mbuna tear him apart while he is younger (depends on the mbuna).