Wow, as a longtime student of TV history & trivia, I can’t believe I hadn’t heard of this before tonight. - Here is the original, unaired pilot of Three’s Company (from at least a year earlier), originally written by M*A*S*H head writer, Larry Gelbart. 

John Ritter & the Ropers are still part of it, but most of the characters names & back-stories are completely different. And no Joyce Dewitt or Suzanne Somers… in fact those characters are completely different.

This is Part One, Part Two is here