If you can find a copy of the Historical Aviation Album, Volume XVI produced by Paul R. Matt, published in 1980, it will have probably one of the best articles on Howard Hughes and his Hughes Racer.
31 pages, lots of photos of the aircraft and details including landing gear, cockpit, engine installation and other interior details. Includes 6 full pages of 3-views giving details of both the short and long span wings built for the airplane.
Keith