The mutants were played by members of the Los Angeles Lakers.
Forrest J. Ackerman's cameo appearance led him to make numerous cameo appearances, and even do bit parts, for more than 40 years.
Peter Strudwick personally contacted Ib Melchior about possibly playing the role of a monster in this film. After visiting Melchior at his house, Melchior wrote the part of The Mutant for Strudwick to specifically portray.
Producer Ray Dorn "borrowed" much of this movie for Journey to the Center of Time (1967). Irwin Allen also borrowed much of the concept for his TV series The Time Tunnel (1966). Director Ib Melchior declined to make waves so he would continue getting work in Hollywood.
The film inspired the TV series The Time Tunnel (1966) as well as the remake Journey to the Center of Time (1967).
Forrest J. Ackerman: In addition to being the editor of "Famous Monsters of Filmland" magazine, also happened to be writer/director Ib Melchior's literary agent.