The "M" in the serial number means the frame was made in 1984. In the late 70's through the 80's, the serial numbers went year-sequential by letter. So, the model could be 1984 or 1985- My bet is on 1984, but a quick scan of the catalogs would tell you for sure.

Nice bike, BTW. I have a 1984 Univega Gran Turismo that's virtually identical. The 80's Univega's were made by Miyata and followed the same serial number convention.