Hi. I was just reading a copy of the "Godfather Companion" by Peter Biskind which gives a bunch of trivia about the 3 Godfather movies.
Anyhow, on page 19, under the title of "On Location", it mentions that the scene of "The summit meeting of Mafia bosses was held in the boardroom of the Penn Central Railroad over Grand Central Station on the thirty-second floor."
Found this kind of fun! Mike