It was the last aircraft designed using a slide rule and conventional drafting --- the conventional wisdom is that if one printed up a compleat set of blueprints and loaded it on the plane it would be too heavy to take off, though of course, the anticipation was that it would soon be replaced by supersonic passenger aircraft, so it was designed to be easily converted to cargo.

Amazing aircraft, well-deserving of the "Queen of the Skies" moniker, I can still vividly remember going up to the upper deck and cockpit and the view out of the front/side windows.