Here are the covers to the British magazines I mentioned.
Super Thriller Annual 1958 (obviously swiped from FC 488):
and Super Thriller Annual 1959, with the same character, same costume, etc.:
The question is, was this second cover an original work for Super Thriller, or was a it a swipe as well from an unpublished fourth John Carter FC cover? The fact that the unpublished Manning issue should be the fifth in the series, makes the latter scenario more plausible I think. I know I'm probably the only one who cares, but I find it interesting nonetheless.