Hanging on the wall in Driscoll's office is a certificate bearing the symbol of the U.S. Army's First Infantry Division - the unit that Samuel Fuller served in during World War II and depicted in The Big Red One (1980). The same type style for the infantry's numeral "1" is also featured in a reading campaign poster in front of National Accounts, the gangster headquarters building. The certificate is for the 16th Infantry Regiment in which Fuller was a corporal.
Though we never actually see inside the main location other than the backroom where the safe is, this is one of the first movies with an Espresso Bar which was somewhat new back then. In fact, several characters keep repeating the fact that ""all they do is sit around and just drink coffee" to punctuate how strange this kind of business is, that one day would become commonplace.
Gus' car is a 1960 Lincoln Premier Landau sedan. It was one of the longest and heaviest production cars ever made.
The song used throughout the film is called Molly Malone.
When Tolly goes to Gela's home and is walking up the sidewalk to the front door it is the Cleaver residence from "Leave It To Beaver". That house was being used in the series during the filming of "Underworld USA".