I could be mistaken, but they look to be Hydro-Gear units. you need to get a light and see can you read any numbers on the label/s.
At any rate, that is not a "plate". It is the charge pump. You pull it off and it should have an O ring sealing it. It also has the pump gears and a small spring and ceramic ball check valve that absolutely has to go back in the correct place and order. Also the pump hsng has to go back the same way.