On-sale date from Comic Reader #100.
Reprint adjusted slightly on last page: When DC added the "SOMETHING BIG IS COMING FROM DC IN '74" blurb at the bottom, they shortened the middle tier of panels at the bottom. Invisible Kid's caption was changed from "There you have it... the origin of the Legion! I'm Invisible Kid... the current leader... saying you should read the other stories in this 80 Page Giant to learn more about the Legion and its members!" to "... I'm Invisible Kid! I and the other Legionnaires cordially invite you to the biggest Legion doings yet... including a wedding of two members! It's in the gala 200th issue of Superboy and the Legion of Super-Heroes... on sale the 4th week in October!". Colossal Boy's upraised hand also went in front of the word balloon originally. (Info from Peter Croome and Allen Ross, October 2008).
Includes an article about the origin stories of the Legion of Super-Heroes and Blackhawk with letters of comment from Joe Filice, Maurice Kane, James T. McCoy and Rich Ludwig.