This was apparently an unsold pilot for a new series. It explains why the entire introduction and credits are different. Only Robert Fuller was in the credits or in the show.
The opening credits of this episode from 1960 copy closely the opening credits of the 1946 film, "My Darling Clementine", starring Henry Fonda. That film also featured the cast names and other information carved or burnt into wooden signs and the post on which they are attached swivels as the camera moves down to the next sign.
In the Complete Season One set issued by Shout!, this episode has the usual theme and credits. In addition, the four regulars appear in the last scene.