I had one of these apart just recently. Trying to remember...
I'm almost certain you have to first push the end platform out (away from the center of the car). There are thin tabs extending from the platform which (if I remember rightly) pass through a hole in the tab that projects out of the carbody and thru the caboose floor. The tabs holding the platform are black, and lay flat against the underside of the caboose floor, so they are easy to miss.
