This looks like the European Yanmar water pump. Note the slot in the impeller shaft and the screw in the impeller. This version also has a reusable O-Ring to seal it up, whereas the Japanese version uses a gasket that needs to be replaced with the impel

Definitely the European model. Note the groove for the O-ring. Why was it disassembled this far?

It made it easier to change the impeller by removing the pump from the engine.