Without knowing the horsepower, and going strictly by serial number range, this engine would be a 1979 - 1980 year model. To be completely accurate in determining a Mercury year model, you need to know both horsepower and complete serial number.
In order to answer this question, the horsepower rating of the motor has to be known. Mercury outboards use the serial number, and horsepower, to determine year model.
Looks to be a 1983. I found this looking for a part for my older Merc. It's a cross reference from serial number to year. http://www.marineparts.com/PARTSPAGES/techhelp/TECH15.HTM