Smith's car is a 1950 Chrysler Windsor DeLuxe limousine. Only 174 were made.
Irwin Shaw's story was first optioned for filming by Alfred Hitchcock, but he chose to make The Wrong Man (1956) and Vertigo (1958) instead.
During the mid-50s, Orson Welles was briefly involved with this project as a potential director and worked with Charles Lederer on a version of the script; this was not used for the final movie.
The aircraft used on the smuggling run is a Beechcraft Model 18 (popularly called the "Twin Beech"), manufactured in large numbers from 1937 to 1969 by the Beech Aircraft Corporation of Wichita, Kansas. It has a fake Egyptian registration code SU-AAC, which was painted over its real one - N89356. This is visible under the left wing when the Italian authorities approach the plane in Sicily. This same plane was used in Cat on a Hot Tin Roof (1958).
According to a contemporary article in the New York Times and The Hollywood Reporter, Orson Welles was originally signed to direct this film.