TonyM, Has anyone made note of "The Long, Long Trailer" with Lucille Ball & Desi Arnez? Here's a youtube of the mountain sequence, in which the '53 Merc magically morphs into a '53 Lincoln. Movie makers think the public doesn't know the difference with details like that, but this goof made the newspapers as soon as the movie came out. Seems the Merc couldn't cut it on the mountain and they had to bring in the Lincoln to pull the trailer.
https://www.youtube.com/watch?v=Ib23273MgHQ