The story you're thinking of had no gangster involvement. FFC had to overcome studio chief Robert Evans' objection to Pacino. But, when FFC finally prevailed, he found that Pacino's agent had signed him to be in MGM's "The Gang That Couldn't Shoot Straight," which would have precluded him from appearing in GF. Paramount's and MGM's lawyers argued for a week and reached a settlement: Pacino would be released from his commitment to "Gang" in return for Paramount releasing Robert DeNiro, who had been signed to play Paulie Gatto in GF. What a break! Impossible to imagine the Trilogy without Pacino; equally impossible to imagine DeNiro, killed off as Paulie in GF, returning as young Vito in II.