The Golden Warriors; the kid that visits Brando on the roof wears a jacket w/Golden Warriors across the back. There was an Italian Street gang at that time (1950s > early 60s) called the Golden Ginnies in South B'klyn which is where the action was supposed to be based.
Charley Malloy, Rod Steiger's character was obviously Eddie Mcgrath, the guy who controlled the West Side Manhattan rackets at the time.
Father John M Corigan, the real life priest father Barry was based on in the film, was also based on the West Side Of Manhattan. This is the core of the film right here.
It was loosely based around corruption in Manhattan and Brooklyn but the West Side certainly influenced alot of the key characters even if the precise location is never really pinned down in the film.
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