Thanks Dave for your kind comments and the link to the museum replica. This is where confusion arises, my book is telling me that the fuselage frame was constructed of four rectangular milled Ash or Oregon pine longerons connected to each other by ash struts. Internal cockpit photos of the replica are showing a metal tube frame. I will be following the book as it has archive photos showing that the fusalage frame was definitely timber. The museum photos will be very useful for adding extra details which are missing from the book. Thanks again Dave for the link and the image of the 1:48 scale model, all very helpful.
Des.