Question about a mixed metaphor and the argument from causation

During this morning's _This Man is You_ video, Dr. Peter Kreeft use an analogy of a freight car to explain St. Thomas's argument from causation (one of the famous five proofs). He said that when you come to a train tracks and see a freight car moving, you know that the one in front of it is pulling it and the one in front of that is pulling it, etc. until you come to the engine which is pulling all of them; and this is like God creating the universe. Now, since this is a men's group, we naturally got to talking about trains and one of the fellows mentioned that it's common to have engines in the middle out west and also common to have them at the rear. And I got to thinking, is God the prime mover puller or pusher? Does that make a difference? And, just to frame this as a question that I think is on topic and not purely philosophical does the Thomistic principle of God as the First Cause also work if you think of God as the Final Cause - does it make any difference; could God also be _all_ the causes?