Although most of Akira Ifukube's score is replaced in the American version, if you listen closely enough you can her a version of what would become Rodan's theme in the Godzilla films from the 1960s.
In the Americanized version from 1962, even though the film is called "Varan the Unbelievable", the monster is called "Obake" throughout the film for some reason.
This was originally supposed to be a co-production between ABC and Toho. However, ABC backed out just before production began.
This film was so heavily altered for the American version that the stars of the original Japanese version, Kozo Nomura and Ayumi Sonoda, are only briefly seen as "Paul and Shidori Isoh." Koreya Senda's part has been completely removed.
In the U.S., this was distributed by Crown International. It was released at the bottom of a pre-packaged double feature with the East German/Polish co-production "First Spaceship on Venus." It became the most successful double feature for Crown International since, unlike other Crown International releases, it was booked into many theaters as well as drive-ins.
The American scenes were shot in Bronson Canyon just outside of Los Angeles. Interestingly, this somewhat bothered Myron Healey who thought he was going to shoot his scenes in Japan like Raymond Burr supposedly had for Godzilla, King of the Monsters! (1956). Interestingly, when Healy appeared on an episode of Perry Mason (1957) he talked to Burr about it and Burr admitted that all his scenes were shot on a soundstage in Hollywood.