You sure? I read at some point that the street parade sequences were shot early in the filming, before it was a sealed deal that Castellano was not coming back as Clemenza.

Looking at GF II in retrospect, you almost have to believe that it was the intention of FFC and Puzo to bring back Clemenza and work through the story line where he would eventually betray the family.

It turned out of course that Pentangeli was the character they wrote into that role, but IMO that kind of wasted the back story scenes of Young Clemenza (Bruno Kirby) becoming tight with Vito and actually leading him into the life of crime.

If their intention all along was that Pentangeli was going to be the guy who rolled over, they could have cast Kirby as a Young Frank Pentangeli and reduced Pete Clemenza to a more peripheral character.

To me, it is clear that after the actual start of filming of GF II, the focus of the story line changed due to Castellano's bailing out. Had they known all along that Clemenza was going to be out of the picture for most of the 1958-59 sequence, they wouldn't have devoted all that time to him in the back story.