Your going to invest as much time re-making that smoker as building a new one. I would add a stack at the top of the chamber and simply plug the old one off for now. Try it with the stack at the top to see if that configuration lets the hot spot escape. If it does not work you only have a hole to plug.
I forget...Have you run this pit with the stack wide open and controlled the temps from the intake only to see if that lets things flow better and even out? If that has been done moving the stack is the next logical step.