Only tryout issue. In Amazing World of DC Comics #10, in the article "There's No Cases Like Showcases" by Jack C. Harris notes: "It is an interesting aside that Jonny Double was originally the hero who later became Chris Chance - The Human Target - who appeared much later in Action Comics." This seems a long shot, given that Jonny does NOT assume his client's guise to prevent an assassination (the Human Target's gimmick). Harris adds, "Jonny didn't get his own feature or magazine, but he did become a "floating" hero turning up in Supergirl and Challengers of the Unknown stories." Later Jonny got a three-issue Vertigo series as a beatnik detective.
Inside back cover, black and white