it is a 12' alum. row boat with the serial # str6820dm751-f. in the process of restoring it and was just wondering the year.
Typically, the model year is built-in to the HIN number ( what you refer to as the serial number is the Hull Identification Number). Its often, but not always the last two digits of the number, so in your case 1975. But to be sure check with Starcraft. You will find their contact info at the end of this article:
Good Luck on the resto!