Number six in a series--collect 'em all!!
Nick Caputo believes this is an unused splash page that was originally intended for the Gunhawk story in Western Gunfighters # 1. That splash page was drawn by Herb Trimpe, with the remainder of the story by Roth/Sal Buscema. Nick suspects this was incorrectly attributed to Hartley. For more info check Nick's Blog:
http://nick-caputo.blogspot.com/2013/02/hidden-gems-in-marvel-reprints.html