It's from 1978, not much CGI going round at that point in time I suspect. Also, you can see the whoosh in their racing suits when the car passes. Also, it was a response to a Holden commercial, where they were driving around cones (witches hats). With all the Ford-Holden rivalry, I seriously doubt they would respond with a fake.
And also, I think Moffat talked about filming it in an episode of V8 Xtra or something