The album in which John Gatchell collaborated with Paul Simon in 1981 was performed in front of how many people?
John Gatchell:  Gatchell was among the musicians hand-selected by Paul Simon, who chose whom he considered to be the finest studio musicians for the 1981 "Simon & Garfunkel Concert in Central Park" The Concert in Central Park:  It was recorded in September 1981 at a free benefit concert in Central Park, New York City, where the pair performed in front of more than 500,000 people.
more than 500,000