I missed the machining of the crown. The CNC shop will love you making their next boat payment unless they owe you a favor.
With a 3.5 mm thick face plate for the dropout, why not divide all thicknesses a bit and just trap the segments from both sides?
When I was messing around with a few frame designs, one solution I used was to introduce bends to the dropout to match the center lines of the stays. (Typical Campagnolo ends have some pre bend) That way the slot the dropout inserts to will be aligned with the center lines of the stays.
Much later I see now a few builders design slots in the dropout so that the stays do not get slotted, the thicker dropout traps the undisturbed "tube".