” Lockheed Flatbed ” concept late 1970’s . The idea was it could carry outsize cargo but also mount a modular cabin for passengers or normal size cargo . About the size & weight of an Airbus A-300 .

While drag was a major concern for carrying exposed cargo, a joint Lockheed and NASA study suggested the concept was technically and economically feasible, with aerodynamic penalties considered a trade-off for specialized heavy-lift capabilities . by SevenSharp