On-sale date per Comic Reader #126, as well as a scan of The Amazing World of DC Comics #9 on Rob Kelly's Treasury Comics website. Also, the Marvel UK comics of the time bear this out, as they run back-cover ads for this title on the issues dated "week ending Jan. 10, 1976" and "Jan. 17". As the British Marvels were published at the actual time of their cover-dates, this confirms that this title was on sale in the UK during January 1976.
Credits based on interviews conducted by Daniel Best for article available at Adelaide Comics and Books website [accessed 26 August 2009]. Official credits in publication are "drawn by" Andru and "inked by" Giordano. Splash page reads "Presented by: Carmine Infantino and Stan Lee"; this was changed to "Edited by" in the 1991 Crossover Classics collection, but no primary editor is given in the original. Conway told Steve Cohen that he "did the actual editorial work," i.e. "proofing, supervision of production, supervision of art and lettering and coloring" [via Facebook 4 September 2009]. Lee's introduction says literary agent David Obst "started the entire project". DC/National production manager Sol Harrison "co-ordinat[ed] the project" with the assistance of his Marvel counterpart Sol Brodsky per Infantino's introduction.