The announcer in Hopkinton at the start of the marathon says "Welcome to the 53rd running of the Boston Marathon". The 1954 Marathon was the 58th running.
The actual winner of the 1954 Boston Marathon was Veikko Karvonen from Finland. His finish time was 2:20:39.
The movie is set in 1954. When Chester is in the Public Address Room, the calendar shows April 1955.
The movie is set in 1954. At the marathon, the people are waving 50-star U.S. Flags which weren't adopted until 1960, with the admission of Hawaii as the 51st state.
The marathon route looks nothing like the true course, even considering the time period. There is no turn out of Hopkinton at the start, the final turn at the finish is a left--not a right, and the hill does not drop off to the right of Heartbreak Hill.