The ExR car would take some work but it's doable. BLMA trucks with FVM 28" wheels might lower it enough where the bolster won't have to be modified. But the body/flatcar is one piece, so the VAP has to be cut from the flat. The flatcar placards also are very thick, and need to be sanded down or replaced. Hiding the weight would be an issue, with an open auto rack hovering above. But it's better than starting from scratch. I haven't looked at the model in a while, but it might be possible to cut out the floor and replace it with a brass or steel slab. Then you have the decent flatcar detail as a four-sided open box to secure the metal slab to, giving a foundation to build the auto rack above it.