If you have the Rivarossi model (#1633), the difference in the cab is the rear overhang. Can't say whether the Hornby model supplies two cabs.

The Alleghany made by Rivarossi had the road #1633 on both cab versions (long & short). The new model (by Hornby) uses road #1629. Haven't seen the new version, so I can't say if there are two cabs included. If there are two cabs, I would think they both would have the same number.