Along with The Last Son of Krypton: Part I (1996), this is one of only two episodes in which Superman does not appear. Clark Kent is only seen as a teenager in the 1980s.
Smallville featured a similar story (three Legionnaires go back in time to help a young Clark Kent fight off Brainiac) in the season eight episode "Legion" (written by Geoff Johns). "Legion" featured Saturn Girl, Cosmic Boy, and Lightning Lad (who replaced Chameleon Boy in the animated series' version, possibly because at the time of the show's production Lightning Lad's early-1990s' character was Live Wire, which might have been confused with the original antagonist created for "Livewire" two seasons before.).
This episode takes place in 2979 and somewhere between 1979 and the early 80's. Although a specific year is not given, it's possible they went back as far as 1979 because that would put it at exactly 1000 years prior to the given 2979 date, and the Dukes of Hazzard reference would still be valid as that show premiered in January 1979.
The scene in which Clark throws a tractor is a reference to the front cover of Action Comics #1 (April 1938), in which Superman made his first appearance.
This story differs from the comic book story by replacing Lightning Lad with Chameleon Boy.