Alan, have you actually talked with one of the Northshore principals. Yes, they no longer build the boats...but surely they have retained the design work. Perhaps it's a matter of reaching the right person? And perhaps knowing who that is could come from the owner's association, if it's not apparent to you.
If that fails, I think you can deduce what you want to fair accuracy by using Dave Gerr's The Nature of Boats.
About Dave Gerr