There's a version of the Trilogy on VHS tape called the "25th Anniversary Collection." Each film begins with some commentary. GF begins with a comment by Puzo, who said, "I heard that Danny Thomas wanted to buy Paramount so he could play Don Corleone. I was disturbed by this [probably the understatement of the decade, IMO!]. So I got Brando's address from my agent and wrote him about playing Don Corleone. I didn't think he'd be interested. But I was surprised when he wrote back and said he was interested, but he'd have to wait until they announced a director."
And you thought Burt Reynolds and Robert Redford were close calls?