Are you sure it's an FM? Cuz for some strange reason, I think it might be a Castle Of Frankenstein. Here are the covers, at Mike Scott's amazing Monster Magazines site:
 http://monstermagazinegalleries.blogspot.com/2009/09/castle-of-frankenstein.html  
If nothing rings a bell, there's a list of other magazine covers on the right side of the page. A wonderful site in general.

D'Entre les Morts,

Richard J. Schellbach