This confusion is a direct result of having two challenges going at the same time. S'land correctly identified chiglet's challenge at the Boeing XF8B. dazdaz's challenge is indeed a Convair 990. Anarchy rules! (an oxymoron, I know).
Tough trivia dazdaz! The 880/990 series was briefly known as the 600, for their 600-mph speeds, but was never marketed under that appellation.
Here is a Convair 600:
