You need to take another look at the serial number since the build record for 151721 shows a 16 foot long square stern. The information at http://www.wcha.org/forums/index.php?threads/791/ may help. Please post some pictures here of the numbers from each end. Thanks,
Congratulations, the Old Town canoe with serial number 161721 is a 15 foot long, CS (Common Sense or middle) grade, fifty pound model with a keel. It was built between February and May, 1954. The original exterior paint color was dark green. It was shipped on June 8th, 1954 to Pittsfield, Mass. A scan showing this build record can be found by following the link at the attached thumbnail image 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/catalogs/old-town/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/about-wcha to learn more about the WCHA and http://www.wcha.org/store/membership to renew.
It is also possible that you could have another number or manufacturer if this description doesn't match the canoe. Feel free to reply here if you have any other questions.