When Perry Mason asks for an address, he is told 1040 Las Palmas. That's the address of Las Palmas Studios, where some Perry Mason shows were filmed.
The opening scene takes place at the Knickerbocker Hotel. There was a Hollywood Knickerbocker Hotel that operated from 1929 until the late 1960s, when it was converted into apartments. The hotel had a rather morbid past. D.W. Griffith suffered a cerebral hemorrhage in the hotel's lobby and died on the way to the hospital. Hollywood costume designer Irene Lentz, apparently despondent over Gary Cooper's death, committed suicide by jumping from an 11th story window. And William Frawley suffered a heart attack outside the hotel and died in its lobby. In 1970 it was converted into housing for senior citizens.
Sometimes "Perry Mason" filmed at 1040 N. Las Palmas in Hollywood. The show also filmed at the 20th Century Fox main lot on Pico Boulevard, and at 1416 N. La Brea. That last address is notable for several reasons. The studios there were originally built during the silent era to be the Chaplin Studio (where many Charlie Chaplin films were made), and in the late 1990's/early 2000's it was purchased by Jim Henson Enterprises and became the Hollywood home of The Muppets.
When Lt Tragg arrives at the studio to confront Perry and Lou Caporal, he and his partner are driving a '59 Buick Electra 225 hardtop sedan. LAPD detectives used only bare bones economy sedans and not high-end luxury cars. This was a marketing ploy, as Buick was a sponsor of the series. Caporal's car is a Buick LeSabre convertible.