Yeah, and even more, they went to all the trouble in the "Young Vito" scenes to set up the back story of how Clemenza and Tessio first hooked up with Vito, and we never see the Pentangeli character at all in the flashback scenes.

At the end of GF I, of course, Tessio betrays the family and is whacked as a result. The perfect parallel in GF II would have been for Clemenza, after 40 years of being the caporegieme under Vito and then Michael, finally giving in and betraying the family at the end.

If Castellano wanted too much money I don't know wny they didn't just cast Gazzo as "Pete Clemenza" rather than "Frankie Pentangeli."

Gazzo was an old balding portly Italian guy, he could have played the role of Clemenza, and instead of having about a dozen irritating little plot points messed up as a result of switching the characters, the audience would have taken 10 seconds to think "Huh, OK, Clemenza looks a little different" and then not worried about it after that.

They didn't have any problem recasting the role of Vito Corleone when circumstances made it necessary, why was recasting Clemenza (and later, in GF III, Tom Hagen) considered such a sacrilege?