The railroad and train are fictitious (although it takes the Santa Fe route), the station scenes when it’s boarding in Chicago are filmed at LA Union Station, and the external shots of the train vary from Pennsy steam to SP Daylight steam, yet the 1952 noir film Narrow Margin takes place almost entirely on the train and gives an accurate feel for the trip in the late forties/early fifties.
The lounge car below is on Union Pacific, but the lounge on the film’s train brought this picture to my mind. In the film one of the characters says, “Meet me in the club car.” I recall my grandmother talking about club cars on trains, and some timetables used the term club-lounge all the way up to Amtrak time, 1971.
The closest I can come to a real train that might match the one in the movie would be the Santa Fe Chief, when it left Chicago in the afternoon and arrived LA on the second morning. It was sometimes hauled by steam post-war, although most if not all of its cars were stainless steel streamlined whereas many of the cars shown in the film are heavy-weights.
Ad above from a 1952 National Geographic. 1948 photo below by Charles H. Kerrigan, reproduced here from a Vanishing Vistas post card, shows one of Santa Fe’s few streamlined steam engines.