The Orthodox stance was used by the last boxer in what weight class to hold the undisputed champion title?
Orthodox stance:  Many boxing champions—such as Jack Johnson, Anthony Joshua, Marco Antonio Barrera, Rocky Marciano, Ingmar Johansson, Roberto Durán, Floyd Mayweather Jr., Muhammad Ali, Amir Khan, Peter Buckley, Johnny Tapia, Mike Tyson, Larry Holmes, Lennox Lewis, and Wladimir Klitschko —fought in an orthodox stance. Lennox Lewis:  He is a three-time world heavyweight champion, a two-time lineal champion, and remains the last heavyweight to hold the undisputed title.
heavyweight