Cover art credits provided 2006 by Nick Caputo.
Image from Fantastic Four (Marvel, 1961 series) #26, splash page.
Transformation images taken from early issues of Hulk comic.
House ad for Marvel's Greatest Comics (Marvel, 1969 Series) #29 (December 1970) and Thor Special (Marvel, 1966 Series) #3 (January 1971), with covers shown, and both advertised as "Now On Sale".