What does 51.5 refer to? There were no 1/2 years in 1951. There were some late model differences due to the Korean war, mostly cosmetic; painted trim instead of Chrome or stainless. Late 51 may have made a change to a 90 MPH speedometer too. In 1952 the most notable difference would be the door handles, in 1952 they changed from flip outside door handles to pushbutton.