I have a 01 dually with drum brakes and I can pick up a disc brake single axel rear of cheap can I and will all of the brake stuff swap over?

I think you will need the proper proportioning valve to run disks in the rear.

what is its location?

Well...that I don't know...but I hope people will chime in...I am interested in doing this swap also. I think if you search the forum there have been a few threads on it...sorry I am not too much help with this.