The reason Jeff and Margo are desperate to get across the Mexican border is that there was no extradition treaty between Mexico and the United States at the time, and there wouldn't be one until 1980.
The apparatus the girl is in in the opening hospital scene is known as an "iron lung", used to treat severe polio cases during the epidemic of the 1950s. It provides respiration by cyclically varying the pressure inside it.
The Hollywood Reporter and the Los Angeles Times ran contemporary articles on how Faith Domergue was a "protege" of Howard Hughes, who owned RKO at the time. Also notice her resemblance to another Hughes protege - Jane Russell.
After Robert Mitchum's marijuana bust, RKO Radio Pictures gave him work starring in several low-budget film noirs until the bad PR blew over. It did not seem to negatively affect his image and might have helped it.
Jeff and Margo drive away from the airport in a 1949 Cadillac Series 62 convertible. Jeff then trades it in for a 1934 International Harvester C-1 pickup truck (and 50 gallons of gas). An example of the Cadillac, in excellent condition in 2024, could be worth about $100,000.