About 15 years earlier, I had done some work at the VAB and walked around the Saturn IV that was laying on its side there, just as James Burke had a few years earlier. It wasn't there when I worked the above referenced mission. I'm not sure when they moved it, or where it ended up (but it's not in the "rocket garden" at the Visitor Center).
If you mean just the Saturn IV (no B), that was the second stage of some early Saturn rocket. I don't know much about those or if one was ever on display.