This simply outstanding "Marvel Masterwork Pin-up" featuring Spidey and his smiling alter ego Peter Parker first appeared in The Amazing Spider-Man #20.
Note Pete's grin on and tousled hair.
The version of that classic pinup below reappeared in Marvel Tales #30.
Aside from a different color scheme, apparently Stan and the gang decided that Ditko's old rendition of Peter was no longer in keeping with the slicker, smoother, more idealistically handsome version of the character developed by John Romita. So they tapped "Jazzy" Johnny to create a new head, or more likely lifted one from another illustration.
Here's a closer look at no-neck Parker. His smile seems less genuine somehow.