This 1958 Pontiac Chieftain served demonstrator duty for a Freeport, Illinois, Pontiac salesman before undergoing two months of preparation for its second incarnation as a USAC stock car.

It raced in such venues as the Milwaukee Mile and Rockford, Illinois. It was retired from competition after 1962, remaining in obscurity until being discovered in 2005. 

https://www.mecum.com/lots/SC0517-282527/1958-pontiac-chieftain-usac-race-car/