No such pictures from me, but from what I could see, it doesn't look like it is very interesting down there anyway. As for the catchwagon...
At the back end of the catchwagon there is a sleeved pin with a gap ahead of and behind it. Under the center of the train is a more-or-less standard chain dog. Remember how a chain dog works: it's an over-running clutch. If the chain moves forward or the train moves backwards, the dogs will catch on the chain. If the train moves forward or the chain moves backwards, the dogs will disengage and allow relative motion. Okay, so instead of several sets of chain dogs, the Millennium Force train only has one. And instead of a chain with lots of links in it, there is a catchwagon with only one. With the train in position in the station, the catchwagon can pass freely backward beneath the chain dogs, but when it pulls forward, the dogs engage and the train moves forward and up the hill.
In the station, the trains are moved (and stopped!) by pneumatic tires driven by small electric motors. These tires rub against a plate on the bottom of each car. The drive wheels are spaced not quite as far apart as the length of the train, so that from the time the train reaches its parking space on the block brake until shortly after it starts to pull out of the loading station, it is in contact with at least one advancing wheel.
--Dave Althoff, Jr.