Since you asked this question in the "site information" category, look near the top of this page for "Cub Info". Click on it for several categories of information. If you select "what year . . ." you will see a window that you can click on a model and enter your serial number; it will give you the year. Alternatively, you can click on "serial number lookup" and it will show you a list of serial numbers by year.
Had you asked this question in the "Farmall Cub" forum, someone would have just posted it is 1978.
