What was the aerial chase scene plane in 'Murder in the Clouds'?
NC-406N would likely have become N-406N if reregistered or transferred. Since none of the 52 Travel Air 4000's registered nor any of the 6 Travel Air D-4000s still have the NC prefix, I'm guessing this is what has happened.

Tail N406N is listed by the FAA as a D-4000 Registered from 1991 on. If this is what you meant, then yes it is correct. Additionally, the wiki page for the movie does list a "Travel Air Speedwings" [sic] as the aircraft used in the production of the movie. I've not been able to verify if N406N is actually a speedwing vs the other models of Travel Air but a more knowledgeable expert might do so with the serial number: 1337.