On sale date from the Catalog of Copyright Entries, Books and Pamphlets, 1976. Same date given in 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.
First Marvel / DC crossover and second co-publication, after MGM's Marvelous Wizard of Oz. Next crossover is Marvel Treasury Edition #28 featuring Superman and Spider-Man.
According to Overstreet, there are 5,000 numbered issues signed by Carmine Infantino and Stan Lee. Based on information gleaned from several internet postings and sales, it appears that only 2000 copies were in the signed edition. Furthermore, because Carmine Infantino was no longer editor at DC as of the end of January 1976, it appears that only a fraction of the 2000 copies were signed by him (at least from #431 up do not bear Infantino's signature). All copies were signed by Stan Lee. Overstreet's claim of the signed copies being a second printing is not supported by any data on the comics themselves.