Classic Aviator
If I recall well, the Boeing 720 was originally designated the 707-020, but they wanted to make something of the short-haul features of the type and gave it a separate number.
As for the 367-80, again if I'm right, it was given this designation, ie. the Dash-80, as a kind of cover story to allow the competition think it was just another version of the basic 367 Stratocruiser.