Shortly after the bomb is found at Magic Mountain, Demerest gets a phone call at the maintenance office. The sound of the phone ringing is like all the other phones in the film. But the phone Demerest uses is just a wall holder with the receiver, with no bell to create that distinctive sound.
The Young Man places the remote bomb on the first roller coaster underneath the main guide rail of the track, but allows the ride to run several times before detonating it. In reality, the up-stop wheels or side wheels of the next train to pass through the course would have knocked the bomb out of place or destroyed it.
The last portion of the movie at Magic Mountain is depicted as taking place on July 4th but in fact it's easy to tell the filming was done during the winter months. The trees in the park are all dormant.