Checking again, the seller says one end is too faint to read except for the length (17). The first three digits at the other end appear to him to be 397 and the last two are 33, 39, 38, 88, or 99. He says all the threes, eights, and nines look similar. I checked 397 with all those possibilities-- none had sponsons... 3 are 17 footers-- one is an Otca and two are Charles Rivers. The canoes date from 1916. The seller says the engine is dated 1918. I'm also looking at the buyer, in case it's someone connected with a business that might have modified the canoe.
Still lots more number combinations to try!