I tried to get some work done on the router this weekend but all the Thanksgiving family fun made it pretty hard to do. The plan right now is to mill out the back of this 1" plate to save on weight to .300 thick leaving contact areas thicker. The spindle plate mounting hole will act like stiffener ribs I hope. If this fails, I will add some ribs to the outer edge as Peter recommended.
Anyone with a mill knows you spend half your time figuring out how to mount work to the table. I decided to build a two piece vice for the facing operation like this:
The back of the "Z plate":
Layout:
Outside dimensioning: