Right, machining the cover down is out of the question, as I have the midplate and front plate locations locked in. Machining the cover would cause the front plate to be too far forward, so I'm thinking about tig welding a dam around the coolant inlets and outlets so no coolant can bypass the pump via the big void where a mechanical pump would be.
Hopefully I can get the aluminum clean enough to do this. I'll post some pics of what i come up with.