Who's This? Who's Who Vol.X p.18, the group that includes Beast Boy (but not THAT Beast Boy), Evolvo Lad, Gas Girl, Life Lass and Duplicate Boy.
How you could have heard of them: All members did wind up appearing in the 5YL era (five years later). Life Lass as a member of the United Planets militia, and then Lallor fell to the Khunds. Apparently under Khund control, the Heroes appeared in Legion of Super-Heroes vol.4 #48, and #57-58. Post-Zero Hour, a few of them showed up in Legionnaires #49 (Beast Boy and Gas Girl, with the former Arm-Fall-Off Boy, Splitter), while Evolvo-Lad was in another team called Workforce. The Threeboot Legion books made use of Lallor, but only Evolvo-Lad was ever seen, as Brainiac 5's ally, in LSH vol.5 #31 and 36.
Example story: Adventure Comics #324, "The Legion of Super-Outlaws" (Sept.1964) by SF writer Edmund Hamilton and artist John Forte
The story really starts with the brother of Legion reject Jungle King (from Adventure Comics #309) who went bad, renamed himself Monster Master and went up against the Legion with his mind-controlled alien animals, until one of them ate him(!).
He got the better bargain. The Heroes of Lallor might as well have walked into the depowering ray for the all the impact they've had on the 30th century. I guess Lallor really IS a distant planet.
Who else? You'll see more from the "H" volume, but to get to the Heroes of Lallor, I did skip over Hawk Son of Tomahawk on the basis that if you know Tomahawk, it's a no-brainer to understand who he's supposed to be (still... he deserves a shot on the second pass). Harlequin might have made it too, but her role as Green Lantern's wife gave her a higher profile than the three entries I DID select for inclusion in Who's This?