My impression is that the differences are mostly cosmetic. 79 had a two-piece dash and 80 had a one-piece dash. 79 pulled the speedometer from the pto side and 80 pulled the speedometer from the chaincase. 79 had mostly black trim on the hood and 80 had mostly blue trim on the hood. The 80 may have a longer heat exchanger under the seat. Some of our 79 chassis have short heat exchangers. Those are the differences that I can think of at the moment.