The serial takes place in the 1980s. However, a BMW 740i with new V8 engines didn't enter into the production until 1994.
When Joe and Biff sneak into the theater, "Night of the Living Dead" is playing and is about halfway through the movie. When they are behind the screen, you can hear dialog from the beginning of the movie ("They're going to get you. There comes one of them now." spoken by the Johnny character in the movie). Then, after Joe hides the tablet piece, you can hear the Sheriff character talking about taking some dogs to check out the house behind the trees. This dialog is from the very end of the movie. But then they show the movie in progress again, and it's still in the middle.