Trained eyes will recognize that even then, Jim was doing his own lettering. You might recognize the cartoony style from Aparo's first published comic book work, Miss Bikini Luv in Charlton's Go-Go comic book. He had few chances to revisit this sort of drawing for the remainder of his career.
UPDATE: I've confirmed that a series of Aparo ads for various Savogran products appeared throughout 1965 issues of Popular Science! The earliest ones are unsigned, but are definitely Jim's (with his distinctive lettering), and they are replaced in 1966 by generic ads with photos of the product containers rather than cartoon panels. I'll post the entire set as soon as I get the time to photocopy them from the bound editions at the library (and the time to scour each issue more carefully, so that I can be certain to have the entire set...at least the entire set that was published in this magazine).