That's right, Marvel's The Monster of Frankenstein (and from issue 6 on, Frankenstein's Monster) came out a FULL MONTH before the Phantom Stranger's Spawn of Frankenstein back-up feature. And wouldn't you know it? Marvel's latest addition to their horror comics line ALSO started with the Monster found in a block of ice.
Coincidence?! Well, Marvel DID invent this comic book trope with Captain America, I suppose. AND they managed to get the book out first. AND their Frank lasted 18 issues, which while not a Tomb of Dracula level of success, is still better than back-up "Spawn" of Frankenstein.