Power steering

I have a 61 IH bus. GVW 23000#.It has a Chevy 454. I would like to put power steering in it. Does anyone know what kind of steering box would work? I assume that I would want nothing smaller than what was used on 2 ton truck. I assume the pump and steering box must be compatable.
I am converting this to an RV. It would not come close to weighing that much.
Thanks