Welcome to LMF, sorry I cannot help you with identification of the year of your Gilson, I doubt if many of the members here have access to a serial number listing. Maybe if you post a picture we can narrow it down. What engine does it have? Any special markings or model identification?
Again welcome aboard hope you will see and hear more from you in the future, sorry don't know any thing about your gilson but picture would be a good idea for better help