I replied to your other post with some pictures of a Cub Scow. There are differences but some specific items in common make me think this might be some early, prototype version. The mast step looks exactly like the Cub Scows & Hydrostream Fox boats I've seen. It is different from a Butterfly, Chrysler Barracuda or JBW Miniscow. The same with the way the deck overhangs the hull. The rounded cockpit walls are something I have only seen on the Cub Scow / Hydrostream boats.