After IIlya and Angela had removed the ropes, escaped and started the fight to escape in Act 4 the 1960's blue Plymouth Valiant started to roll and go over the cliff. But the car that went over the cliff and burned was a much older model car possibly an early 1950's car and clearly not the same body style.
Solo is attacked by a rampaging bull. They show several close up shots of the bulls horns ramming into objects near Solo. In some of those shots you can see carriage wheels revealing the horns are part of a cart of some sort, possibly something with which bullfighters use to train.
During the Act 4 sequence where the car rolls and goes over the cliff, just before the camera switches to the car going over the cliff the cameraman and lights can be seen reflected on the front bumper. Also camera lights can be seen reflected on the side of the car as it rolls.
During the opening sequence Illya is speaking from the backseat with the driver of the car. When the camera tightens in for close up shots of just Illya in the backseat, the boom is resting across the top of the seat with the mic directly in front of David McCallum while he delivers his lines.