All of the first Mountain Goat frames used the ovalized Phil Wood tandem boom tubes for the top and down tubes. Later, when the Escape Goat and Whiskeytown Racer models were added, this model became the Deluxe. The idea was to give the frame a little more "give" for a little more comfortable ride. This was the "RAD" or Ride All Day philosophy.
More pictures and details @ 1992 Deluxe page (Twitter and Facebook "share" links)