If it has a hull identification number
That will narrow your search. My 1968 doesn't have a HIN. If you check the USCG site you may be able to learn when the Coast Guard established that policy.Have you been able to do a title search? if it has an old registration Number then the state that assigned that number would have record of the boat.Good hunting.Edit to add: I just checked this site and it tells you everything you ever wanted to know about HIN but were afraid to ask.http://www.boatsafe.com/nauticalknowhow/hin.html