I'm sure the quick-draw shootout opening scene was added later. I'm remembering way back here - it was 1955 and I was 9 years old, living in Beaumont, TX. I'd seen the John Wayne intro and was eager to see the first episode of the new series. I've long forgotten the story of the first episode, but the way I remember the opening sequence of the first season was a montage of guns being drawn and fired. No faces visible, just hands going for six-shooters, drawing and firing. Different costumes, obviously depicting different men, different holster rigs and cartridge belts, at least one beginning with his back to the camera, turning and drawing. The producers may have thought this was too violent and put too much emphasis on gunplay, though when you name a show "Gunsmoke" you sort of expect that. Anyway, the mainstreet shootout began with the second season or later.