I have seen of the double ended skiffs that were so common in the shallow lakes of Wisconsin, (Butte des Mortes, Winnebago, Poygan). Ron Koch, author of WHISPERING WINGS AND WOODEN BLOCKS talks about a fiberglass boat that was taken from a wood strip boat make by Gust Nelow, (better known for his decoys than his boats).
When I got Koch's book about 10 years ago I contacted him and asked him where I might get one of the boats, (his were fiberglass), that he showed in his book. Koch's boats, which bear a striking resemblance to your boat, albeit without the sexy upswept bow and stern were no longer made but that he felt the Hoefgen Canoe most closely mirrored the original model for his boat, (the Nelow strip boat). He was kind enough to send me a picture of an original Nelow boat but I cannot locate it right now. I would have thought that it would have been inside the book but its not there so its sitting in a safe, and unknown, spot. Impossible, of course, to swear that the Nelow boat and your's are "damn near twins", but that was my original thought when I saw the pictures of your boat.
If the 1870's age of your boat is corrent then Nelow could have built it as he was just a baby in the 1870's, (born 1874), and didn't start building boats until 1924 but I'm guessing that he was building from a common design of the marshes around the Oshkosh area.
Check out the Hoefgen Canoe, (I thinkin its hoefegen.com but you can google it if it doesn't), and see if you don't think that boat and yours bear some very striking resemblances.
Anyway thats what I know, which obviously isn't much, but might possibly be a place to start.
Steve