Originally, David Fury had written a darker script called "Corrupt." In that script, Kate was undercover but working as a prostitute, and Angel licked blood off of a murder victim. Copies of the script are floating around on-line.
The phone number on Angel's business cards is; 213-555-0162. The "555" exchange is commonly used in entertainment because it is reserved for information services. This means that no active number will use the exchange. The "213" area code identifies the location as Los Angeles.
Doyle says, "That narrows it down to about, what... 5 million suspects in the naked city?" Naked City (1958) was a TV cop show which aired from 1959 through 1963. Each episode ended with the narrator saying, "There are 8 million stories in the naked city. This has been one of them."