Whit Bissell (General Kirk) previously played George Armstrong Custer in The Broken Pledge (1957). He was actually better played by Ronald Reagan in Santa Fe Trail and, more famously, by Errol Flynn in They Died with Their Boots On. Flynn also appeared in SFT.
This episode takes place near the Little Bighorn River, Big Horn County, Montana Territory from June 25 to June 26, 1876 and in Arizona in 1968.
The background music for the cavalry scenes is "Garry Owen" (or "Garryowen"), a very popular period song that was (and still is) the unofficial anthem of the U.S. Cavalry, especially the 7th Cavalry Regiment, which was Custer's command.
Joe Maross was 43 when he played George Custer. The real George Armstrong Custer was 36 at the time of his death in June 1876.
Less than two months later, guest stars Paul Comi and Lawrence Montaigne would be castmates in another sci-fi series episode, Balance of Terror (1966), a classic from the first season of Star Trek (1966).