At this point, its all somewhat academic. I have (or will, shortly) have 3 bandos/accordions, 2 accordinas, and a piano Vibrandoneon. At some point it becomes an exercise in obsession.I am wondering if what you want can be custom made? If you contacted Bugari, for example, I wonder if they would make an existing converter model with just free bass. Of course, I may be saying this because of my lack of knowledge on accordion design, but I would think it would be possible???