Here in the US, it was just called the GS400L, and they were part of Suzuki's lineup of twins that included a standard E model, a more sporty S model, an economy T model (spoke wheels and drum brakes) and the 'cruiser' L model. Mechanically very similar, primarily different styling.
Great bikes, IMHO, for what they were. Not really sure about differences for non-American markets....
I didn't own a 400, but I did own it's little brother, the GS300L. Super nice little bike - smooth (I think the engine had counterbalancers), powerful enough to haul me around at 65mph and got 70 mpg into the bargain. The bigger twins (400 and 450) definitely had the counterbalancers.
Sorry I'm not more help, but good luck with it.
Kirk