Very obvious double for Sinatra as Doheny follows Magnum and Rick. Shot from behind, the double's hair is much longer in the back than Sinatra's.
When Sinatra fist says Magnum's name in the bar, he says "Magnus." The name "Magnum" was dropped in during post production.
The photo and small video clip of the little girl on the swing in New York City includes tropical vegetation not found in New York parks.