The only thing missing from Godfather II was Clemenza, I didn’t particularly care for Pentageli.
I liked Frankie "Five Angels", but Clemenza would have been better - but he (Richard Castellano) insisted on allowing his girlfriend the ability to edit his lines in Godfather II, and Coppola refused and wrote the part out of the script and replaced him with Pentangeli.
Clemenza was the highest paid actor in I. Asked for too much in II, so they canned him.
Hyman Roth was based on Meyer Lanksky.... Russian Jew mobster who financed Italian Mafioso. Bugsy Siegel is Moe Green. 80-90% of the movie was barely re-written truth based on well-known Mafioso. The Cuban scene happened; cut real short in the movie. Great Havana casino was built and thrived with Hollywood performers for a short bit. Sinatra et al were in on it. That's where all those beautiful old 50s cars came from. Cuba was incredibly ritzy for a year; lawless city of decadence.
Castro came in with his uprising; seized it all, banned gambling...etc.