An often-overlooked issue by Dennis O'Neil is JUSTICE LEAGUE OF AMERICA 75, Nov 1969. The story where Green Arrow/Oliver Queen lost his fortune, and became more man-on-the-street socially conscious and liberal.
https://viewcomiconline.com/justice-league-of-america-1960-issue-75/That was just 6 months before O'Neil and Adams began their famous run in GREEN LANTERN 76, April 1970. And kind of set up Green Arrow to be the liberal side of the conservative/liberal dialogue between the conservative Green Lantern, and the now more socially liberal version of Green Arrow.
https://viewcomiconline.com/green-lantern-1960-issue-76/I doubt when O'Neil did JLA 75, that O'Neil imagined just 6 months later he'd be teamed with Neal Adams to do the GREEN LANTERN series that would expand on that.
I suspect that it just randomly evolved from editor Julius Schwartz pairing the two as writer and artist on GREEN LANTERN, in an effort to increase sales on the series by taking it in a new direction.
And happening just after Schwartz had paired O'Neil and Adams to do the same with Batman in DETECTIVE COMICS 395, cover-dated Jan 1970, just 3 months before beginning their new GREEN LANTERN series.
