The CHN is the old code for a Chestnut although the information at http://www.uscgboating.org/recalls/mic_detail.aspx?id=CHN confirms that this code is now being used by "CHEM TAINER INDUSTRIES INC." The information at http://www.boatsafe.com/nauticalknowhow/hin.htm indicates that the "76L" shows that it shipped in July, 1976. There are no known serial number records for the Chestnut Canoe Company so additional information is not available at this time. Sorry,
Keep in mind that by the time your canoe was built, Chestnut had been competing against aluminum canoes for 32 years, Royalex canoes for 17 years and fiberglass canoes for 11 years. Raw materials were getting harder to find as well. It is not surprising that they had to cut corners to try to survive (which they didn't - they closed their doors 2 -1/2 years after your canoe was built).
Construction issues aside, Chestnut designs remain among the best that were ever built.