Open cabs were by far in the majority on these engines. Locos were built for specific tasks or routes at the time and it appears those of this class fitted with full cabs were initially intended for passenger working. There were a few variations in cab shape too arising in the closed version (I think) from those that were modified against new builds, plus the shape of the cutaway on open cabs also showed some variation.
To back-date one of these to the original design would require some surgery, round-topped firebox, Salter safety valves and a different smokebox door with continuous handrail. Mind you, this configuration (apart from the front-end) was still common in LMS days and, on a few locos, into nationalisation so it wouldn't be a dead-end for production. Red livery (lined too) for goods engines was discontinued in 1907 and from photos, it looks like the repainting schedule was pretty brisk.
It's a lovely engine to look forward to. I hope the guard irons haven't been omitted this time, they complete the shape below the footplate (the only real glitch with the Jinty) and of course it provides another retail opportunity for the suppliers of enginemen.