This is the 28% Ultimate Biplane by Darren Bowman, not to be confused with the Carl Goldberg 54″ Ultimate by Dave Patrick. This Ultimate has a 10″ greater wingspan.
This plane has birch ply fuselage sides, top, and bottom, and balsa wings. The fuselage is over 48″ long, so the fuselage sides have a joint in the radio compartment. The lower part will be bridged by the wing saddle doubler. The upper part probably needs some thick balsa sheet, or a piece of ply, or something. The fuselage top bridges the joint, as do the top deck stringers.
George Wallace built one of these and was kind enough to send his bill of materials and a few helpful construction tips, which can be downloaded here.