This display model was sold on EBay couple of years ago.
Without a display stand it’s difficult to determine exactly who made this, but all indications are that it was an “official” model, made by Boeing, Lockheed or NASA.
The design was given some small amount of study around 1973, though the available documentation on it is lean.
It competed against Lockheed’s first twin fuselage C-5 concept.
Of course, the C-5 would have been easier to modify since it already had shoulder-mounted wings.