Interestingly, this came out the same month as HULK #3, which also featured a "Circus of Crime". It would be curious to find out exactly what order these were done in. I assume some, but not all, of Kirby's cover-only jobs in this early era were done before any interior work on the issue (thus providing springboards for the stories and character designs). And of course another version of the Ringmaster was a golden age villain for Captain America.
Dick Ayers inks on this cover.