Underworld settings in the USA featured in the movie included Skid Row in Los Angeles and Little Italy and Spanish Harlem in New York City.
In the novel, the main character is called Derek Torry, not Lou, and the entire story is set in the UK.
The unsettling poster Bronson's character has in his apartment is a detail from "Saturn Devouring His Son" a painting by Spanish artist Francisco Goya.
The name of the reclusive hippie monastic religious commune in Carmel in California, USA was the "Ashram of the Circulating Light".
John Ritter and Charles Bronson both passed in 2003 almost two weeks apart. Bronson died on August 30th, while Ritter passed away on September 11th.