Old Town stopped keeping paper records around 1994 before serial number 470000 as shown at http://www.wcha.org/catalogs/old-town/oldtown_chart.html so there isn't a old style build record for number 781608. It should have a hull identification number that starts with XTC on the starboard stern. The information at http://www.boatsafe.com/nauticalknowhow/hin.htm will help you interpret this information including an encoded year. Good luck,
The Old Town canoe with serial number 181608 is a 16 foot long Otca model with a keel. It was built between October and November, 1968. The original exterior paint color was L. C (lemon chrome?) yellow. It shipped on August 11th, 1969 to Convent, New Jersey. A scan of this build record can be found by following the link at the thumbnail image attached below.
This scan and several hundred thousand more were created with substantial grants from the Wooden Canoe Heritage Association (WCHA) and others as you probably know well. A description of the project to preserve these records is available at http://www.wcha.org/ot_records/ if you want more details. I hope that you will join or renew your membership to the WCHA so that services like this can continue. See http://www.wcha.org/wcha/ to learn more about the WCHA and http://www.wcha.org/join.php to join.
It is also possible that you could have another number or manufacturer if this description doesn't match your canoe. Feel free to reply here if you have any other questions. Let us know what you find.