I agree... we needed more McQueen and less Sinatra and Lollobrigida. They didn't convey any chemistry between them in the movie, and they were having a real-life long term "relationship" during 1958-59! This speaks poorly to their acting as well as their real relationship. Peter Lawford also was "involved" with Lollobrigida around the same time, but what are friends for?
And Sinatra was too busy playing cool (maybe to outshine the real King of Cool who was just hitting stardom?). Had Sammy played McQueen's role, as planned, The Chairman could have presided over yet another raucous Rat Pack get-together masquerading as a dramatic movie.
Watch 'Objective, Burma! (1945)' instead!
If one analyzes this movie is a certain way, one wold conclude that the Carla character is criticqal to the success of the story being properly interpreted . . . she's a major force in this film . . .