Dave, what you're seeing is version three. The base originally had a .050" deep dovetail on the bottom and was to be installed adjacent the lock on the barrel. Then I was going to dovetail the base into the tang. What you see is the last version without windage as you noted. I am going to make another upper part with a horizontal dovetail containing the aperture that can be used for windage adjustment as the wonderful German peeps used.
The aperture is .067" diameter and its center is .425" above the upper tang surface.
Dennis