please correct me if I'm wrong , but the Dumas cowl will need to be narrow than a cowl for a newton plan hull. My cowling need to be 4 1/2 inch wide by about 29 inches long. I believe that most of the boats built from newtons plans are closer to 5 inch wide. As for the length on my boat i moved the radio box forward so the cockpit is no longer part of the hull wicth is why mine is that length. I have talked with John Borden about his cowlings and his narrow that what i need but I'm going to see about widen that one to make it work. If you have the kit still just built the cowling as the plans state and use that as the plug to create a fiberglass one.
Take a look at my gallery. i did make a cowl off of the plans i had enlarged but it didn't turn out like i had hope, so i started to redesign some area's
I hope this help.
my gallery