The '64 Lincoln Continental that took the header over a cliff was actually footage pulled from Thunder Road (1958) of a '57 Ford doing a crash and burn, not a '56.
At about the 30 minute mark, the sheriff drives up and you can see on the bottom of the driver's door the faint remains of the word POLICE. That has been removed (mostly) and on the top half of the door, it has a sheriff's logo and the word added.
In one scene, Eula is seen dumping gasoline inside of Barclift's car, yet the AZ authorities put down the crash and Barclift's death as an accident. It would be unlikely that the gasoline cause would go undetected, and it would have created a hot enough fire to destroy the dental bridge that was used for identification...