Chapter1 has some nice shots of the Glendale Grand Air Terminal, once the premier airport in Los Angeles. It still stands and has been mostly restored.
The airplane in which Mandrake takes off from the airport in chapter 6 is Civil Aviation registration #NC15044, a Fairchild 24C-8D, The Fairchild Model 24 is a four-seat, single-engine monoplane light transport aircraft designed by the Fairchild Aviation Corporation in the 1930s.
Opening credits where it depicts the main actors, mainly Kenneth MacDonald and Don Beddoe, starting to laugh, where it seems that someone or persons are having fun or making faces off screen.
One of the very few films in which perennial villain Kenneth MacDonald played a good guy (and even lived to the end).
Mandrake drives a 1938 Pontiac; his associate Lothar drives a 1937 Packard.