This artwork by Sal Buscema appeared on the last page of Defenders #6 (then reproduced as a two-page spread in Giant-Size Defenders #1). Although pin-up pages sometimes felt like filler, this piece did a nice job capturing the early team. While common during the Silver Age, these features all but faded out in the 1970s. The "once-in-a-lifetime" text (reproduced below) that originally accompanied the illustration may not have been exaggerating, as this the first Defenders pin-up page I've seen.
NON-TEAM OF SUPER-DOERS EVER
ASSEMBLED IN ONE GLORIOUS, ONCE-
IN-A LIFETIME PIN-UP PAGE
DIRECT FROM MAGNANIMOUS
MARVEL TO YOU!