There is a Furman Byrd DOB 02/1950 in the 1950 Cleveland U.S. census. He is listed as the grandson of Walter Byrd, 48, widower, a porter at a barber shop by trade, who resided with his son Walter, 19, never married and unable to work, and his daughter Ouida, 20, who kept house. The address of the house was given as 2240 Rear E. 97th, which currently appears to be a vacant lot listed as being owned by the city of Cleveland. One Furman Byrd of Williams HS in Stockbridge, MA received a blue ribbon at the 1968 Boston Globe Art Awards (Boston Globe 02/06/1968). Byrd must have been back in Cleveland by the summer as he is noted to be an exhibitor at an art show featuring inner city artists at the Severance Center Mallon Cleveland Heights in August 1968 (Sunday Plain Dealer 08/25/1968).
An article in the 04/30/1978 Sunday Plain Dealer (Cleveland, OH) mentioned a “Furman Byrd Gallery” at the Collingwoods Art Center on St. Clair Avenue hosting an urban art themed show.
One thing to keep in mind is that the war in Vietnam was escalating around the time that Boyd was presumed to be missing. Perhaps he went to Canada or lived under an assumed name to avoid being drafted.
I wonder if user NRG is in fact Nan Goldin, subject of the interview posted by bmo725. She mentioned in the 2017 interview that she would like to find him.