Car #41 carried a mock-up 'vibration test unit' of the Lunar Roving Vehicle, built for the NASA Apollo program by Boeing.
The 'moon buggies' were used on the last three Apollo mission - 15, 16 & 17 -- to give the astonauts additional range for eploration away from their landers.
The units that went to the moon stayed there. The test article carried aboard the American Freedom Train is now at the U.S. Space & Rocket Center / Marshall Space Flight Center in Huntsville, Alabama, on loan from the Smithsonian Institution.
Research: SR Bush and Ed Stewart II, Director of Exhibits and Curation at the USSRC.