So am I right in saying this is a 'Cow and Calf' locomotive? Because the 'B' unit has an engine, not just traction motors (which would be a 'slug' I think?) In the UK there was only ever 1 locomotive type that had two units like that, which was the class 13. It was just two class 08s weighed down and strapped together with only one cab. Same concept as Cow and Calf, although they called it Master and Slave.