On-sale date from Comic Reader #104.
Captain Thunder is obviously based on Fawcett's Captain Marvel, who had had his own DC comic for a year when this issue was published (Shazam!). DC didn't introduce Captain Marvel into the main DC universe until Justice League of America #137 (December 1976).
Credits for pencils and inks confirmed from Julius Schwartz's editorial records, provided by DC Comics.
The Monster League of Evil next appear in Gotham City Monsters #4 (February 2020).