Hi Ed,
The rumble seat bottom and back cushions are springs only, no wood. The bottom sits directly on the floor. There are a couple of tabs at the back of the floor, attached in the same area of that water dam that is back there on rumble-only cars, and the bottom cushion clips under those tabs and then is located at the front by the metal dowels that stick up from the floor. I may have some pics that would help you understand this if it's not clear enough.
Randy