They used 2 Plymouth Valiant's in the movie one had the slant 6 and the other one had the 318. The gas station scene with the attendant does not show the engine when he opens the hood, but the actual Valiant that Dennis Weaver drove was with a slant 6. But there is one scene where they show the dash and it has factory A/C so I'm guessing in this scene they used the Valiant with the 318.