stock water pump has no plate, water pump housing(timing chain cover) is the plate and the impeller is a distance away from it.
I had a piece of aluminum welded in to the housing. Then then had it machined so that the impeller would just touch it, without the water pump gasket.
Mine is a drag race application and electric motor and belt driving my water pump.
There is a thread over at Moparchat thats called SB Oval Track Cooling. By "sanborn"
He goes into great detail on how to keep a sb mopar cool. GREAT article to read!!!!!
The first thing he talks about is buying the most "efficient alu radiator " you can fit into your ride.