INSIDE FRONT COVER
Inside front cover: A Steve Ditko collage. Upper left: Ditko cover to the fanzine Yancy Street Journal #8, middle left: A panel from Amazing Spider-Man Annual #2, upper right and below: Rare Ditko promo sketches of Spider-Man and Dr. Strange.
INSIDE BACK COVER
Inside back cover: A Ditko sketch from Marvel's Greatest Comics #24.
I always use the original back cover on the customs.