Stop the train...

[axabrax]

Gorgeous weathering and paint! Looks a little late to be an Old West train to me, but what the heck do I know, and who cares with a paint job like that anyhow 

[The Dozing Dragon]

so is 'O' scale approx 28mm?

[Michi]

so is 'O' scale approx 28mm?

Actually itīs 40mm.
But that engine is narrow gauge which is a little smaller than a standard gauge locomotive. But it looks as standard gauge from its proportions and that makes it look perfect for 28mm to me.