You are correct, your hull would be the 35th in that model line. I have the full break out at home. My last 4 are M83A which I would assume has the boat built in Aug of 1982. The book I have states that the boat model year starts in Aug. and the month codes start at "A" so maybe your was the last for the 85 season?
Hank Green
http://members.home.com/hankgreen
Hank Green
http://members.home.com/hankgreen