My worry of bringing in Howley, King, Worsley or anyone who played in that era as a coach is that their status may be diminished if their spell isn't as glorious as the side of the golden era was.
That said, one player from that era who has made a name for himself as a coach is Rob Hoadley. Two Major League Rugby titles with the San Diego Legion and the MLR coach of the year award last year. He recently stood down for family reasons, but no indication whether he'll be staying in the USA or not.