As I've not many sources about Z to dig in, I'll try to reach the correct answer step by step.
I've read that Zbrojovka Brno during the first years (1924-1927), when built MGs under licence, developed a 6c 1000 cc as a racer prototype. I think that may be our car; I haven't found a proper name, but I suppose it was based on the model Disk.
Am I on the right path?