Presumably due to the limitations of the moulding machines used by Nu Cast, the railcar body is supplied in twice and many bits are you might hope. Each side, roof and floor is a pair of parts to be joined by the builder.
First though, there is some light flash to clean from within the windows. When mentioning cleaning up, most people think of files but I prefer a sharp knife for this job.
OK, carving metal seems a bit off but lead alloy is soft and Swann Morton blades aren't, so it cuts like butter. More to the point, the flash is incredibly thin so carving it away is a quick and easy job.
For a really nice finish, the same blade can then be scarped along the edge to finesse and polish any hint of mould lines away.