When Miss Lee approaches Cathy and Blake in the restaurant, Blake is holding a cup in his right hand and places it down. In the next shot, he's holding the cup in his left hand and puts it down again.
Although Mason is shown driving a 1959 Dodge Custom Royal Lancer, the car that goes over the cliff is a less expensive 1958 Dodge Coronet Lancer. And, when it goes over the cliff, extensive front-end damage can be seen, meaning this was probably a wrecked car the studio purchased just for this scene.