Complex sentence: Tunney would go on to beat Jack Dempsey for the heavyweight title, and Greb remain the only man ever to have beaten him, and Tunney would be among the pall-bearers at Greb's funeral.
Split into simpler sentences: Tunney would go on to beat Jack Dempsey for the heavyweight title. Greb remained the only man ever to have beaten Tunney, and the latter would be among the pall-bearers at Greb's funeral.