I have a DT175 that I got from a relatives barn. It was manufactured in early 1980, but I think it might be a 79. How can I tell if it is a 1979 (F) or a 1980 (G)? I assumed it was an 80 but bought a main crank bearing for an 80 and it would not fit. Turns out the 79 and 80 models have different right main bearings but the same left.