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.
It ain't rocket science!
'Course if yer house has more wheels than yer truck...
" Old age ain't for sissies "