The Old Town canoe with serial number 155799 is a 16 foot long, AA grade, Otca model with Western red cedar planking, open mahogany gunwales, a keel, and a floor rack. It was built between April and May, 1951. The original exterior paint color was probably similar to the image at http://www.wcha.org/catalogs/old-town/designs/design43.gif which was known as design number 43. It shipped on June 20th, 1951 to Gaylord, Michigan. A scan of this build record can be found by following the link at the attached thumbnail image below.
The "CS" grade stood for "Common Sense" and this grade is still available today. It was originally the middle grade between the top of the line AA grade and the no frills GS grade. The letters "GS" are presumed to stand for "Guides' Special." The AA grade was discontinued in the 1950s and the GS grade only lasted until the 1940s. The grade description page from the 1951 catalog is attached below. More information like this is available from http://www.dragonflycanoe.com/cdrom.htm on the Complete Old Town Canoe Company Catalog Collection CD.