Per Nick Caputo, Kirby pencilled the cover, although Ditko either did rough pencils on the Spider-Man figure or revised Kirby's original figure. Ditko likely touched up the Giant-Man figure as well, with Chic Stone inking the cover. Nick has an examination of the cover at his blog: http://nick-caputo.blogspot.com/2012/05/avengers-11-cover-mystery.html
Iron Man appears on cover but not in story.
Letters from Thomas Bloyen, John Hudson, Barbara McCasland, Tom Conti, Masataka Hirota, Ruth Doyle, Robert Linderman and Al Russell.