The Old Town canoe with serial number 116547 is a 17 foot long, CS (common sense or middle) grade, Otca model with red Western cedar planking, open spruce gunwales, 20 inch ash decks, ash thwarts, ash seats, and a keel. It was built between November, 1935 and February, 1936. The original exterior paint color was dark green. It shipped on June 8th, 1936 to Augusta, Maine.
The Old Town canoe with serial number 23596 is an 18 foot long, AA (or top) grade, Charles River model with red Western cedar planking, open mahogany gunwales, mahogany decks, mahogany thwarts, mahogany seats, half ribs, and a keel. It was built between October, 1912 and February, 1913. The original exterior paint color was dark green. It shipped on February 14th, 1913 to Des Moines, Iowa. The one with number 123596 may be a better match. This is a 17 foot long, CS grade, Otca that shipped to Jamestown, New York in 1940.
The Old Town canoe with serial number 164781 is an 18 foot long, CS (common sense or middle) grade, Guide model with a keel. It was built between February and May, 1956. The original exterior paint color was G. S. (Guide's Special) green. It shipped on June 7th, 1956 to Winthrop, Maine.
There are 100 records which match your ??781-18 format and about 21 of them are likely to be 18 feet long. The one at
https://www.wcha.org/forums/index.php?attachments/33981/ is one but isn't likely to match. Can you provide pictures of the serial numbers and surrounding areas from both stems?
The Old Town canoe with serial number 28733 is an 18 foot long, CS (common sense or middle) grade, HW (Heavy Water) model with red Western cedar planking, open spruce gunwales, ash decks, ash thwarts, ash seats, a keel, a floor rack, and sponsons. It was built between September, 1913 and June, 1914. The original exterior paint color was dark green. It shipped on July 2nd, 1914 to Winnecook, Burnham, Maine.
Scans showing these build records can be found below. These scans 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 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 join.
It is possible that you could have other numbers or manufacturers if these descriptions doesn't match the canoes. Feel free to reply here if you have any other questions.
Benson