Graham suggested to gain an extra inch or two, I could eliminate the floors for the cabin sole and laminate plywood directly across the center of the hull to build up this area for the required strength; using the top of the plywood as the cabin sole. The thickness of the plywood would be less than the depth of the floors and sole gaining an inch or so in headroom.

Along the same lines, the cabin beams can be eliminated and the cabin top thickness increased until it is self-supporting. This can be accomplished several ways: add plywood layers, make a sandwich with plywood-foam core-plywood, or make a sandwich except use wooden spacers to separate the top and bottom layers (for an I-beam effect).