Beachkoma, the HIN should have 12 digits total.
XDYAxxxxM78m (Joe, the "new" format began in 1984)
I assume you are missing a couple of those "X's"?
m = the letter code for the month during the 1978 model year that your boat was built.
Rudy at D&R may be able to tell you where O'DAY marked the 2nd (hidden) location of the HIN. I believe that manufacturers were required to mark the HIN in 2 places, 1) on the outside of the transom and 2) somewhere hidden from easy view (like under a deck fitting or inside a compartment...... Widgeons don't really have any deck fittings large enough to hide a HIN, so maybe under the forward deck?) In 13 years of ownership I haven't found the hidden HIN on my DS II..... so maybe I'm wrong about that requirement? Gosh...... now I've got another excuse to go over my boat with the proverbial fine-tooth-comb!
What part of Wareham? I sail my 1979 DS II "SUNBIRD" out of Mark's Cove on the Wareham River side of Cromesett Point. Prior to buying my DS II in 1996 I owned a 1969 Widgeon and had SO much fun!! I sold her to a family over in Dartmouth, not sure if they still own her.
Anyway, if you ever need any questions answered about your Widgeon, feel free to ask me (Rudy is the best source...... but he and I have learned much from each other!)
PS: If you saw SUNBIRD you would understand the "SUN" part of her name...... she is bright yellow and the sail is white with a yellow stripe and an orange stripe!
Pictures below of BLUE BIRD and SUNBIRD.