Complex sentence: The superheated versions could be identified by the position of the chimney on the smokebox, with the chimney displaced forward to provide space behind it in the smokebox for the superheater header.
Split into simpler sentences: The superheated versions could be identified by the position of the chimney on the smokebox. The chimney was displaced forward on the superheated engines, to provide space behind it in the smokebox for the superheater header.