Welcome and congratulations, the Old Town canoe with serial number 181621 is an 18 foot long guide model with half ribs, a keel, outside stems, a mast seat, a mast step, a complete rudder, rub rails, and a bang plate along the full length of the keel. It was built between October, 1968 and May, 1969. The original exterior paint color was red. It was shipped on May 16th, 1969 to Juneau, Alaska. A scan showing this build record is attached below.
This scan and several hundred thousand more were created with substantial grants from the Wooden Canoe Heritage Association (WCHA) and others. A description of the project to preserve these records is available at
http://www.wcha.org/catalogs/old-town/records/ if you want more details. I hope that you will donate, join or renew your membership to the WCHA so that services like this can continue. See
https://www.woodencanoe.org/about to learn more about the WCHA and
https://www.woodencanoe.org/shop to donate or renew.
It is also possible that you could have another number or manufacturer if this description doesn't match the canoe. The page below from the 1978 catalog probably shows this canoe and a similar green one from the same trip. Feel free to reply here if you have any other questions.
Benson