It was soon after AMC started supplying Jeeps for Daisy, so my guess is some sort of publicity/sponsorship tie-in. The wheels look similar to Dixie. US motorsports races often have a grand marshal, so they're just borrowing the term for this race. From Wikipedia: "Grand marshal: A person selected at an automobile race (eg NASCAR, IndyCar) by the track owner or race sponsor to be the public leader of events on race day or throughout the race weekend. They may have ceremonial duties such as giving the command to start engines, driving the pace car, waving the green flag to start the race, or presenting the trophy to the race winner." Sadly, the props department rarely spelled "marshal" correctly on cars and uniforms etc. - most occurrences show it spelled like this with two 'l's instead of one.