Delta's were built in Woodlawn IL. I talked with a guy who lives near Lake of Ozarks MO that worked at Delta when he was in high school (circa 1958). The boats were offered as factory built and as kits. He told me that the hulls were made is Wisconsin he thought. My understanding is that the boats with the walk thru between the front seats were for water sking and giving the model name of "Sexy".
My title shows mine as a Sexy and the bow trim was marked on the back "Sexy $35". There is a tag under the deck nailed to the bow marked "SX 344". My boat was factory built and purchased from Buds Place in St. Louis by my uncle in 1957. A couple of years later he traded the 25 HP motor for the Mark 58.
Your boat is trimmed different than mine. The top alum trim is different, the light fixtures are different, rub rails are cut different, and your bow chocks look bigger. My decks don't have the rope trim work.
The cutout in the front seat looks more square than mine. With all the differences I'm wondering if your boat is a home built.