Getting closer!!
I slitted the steerer tube clamp, opened the slot in the middle of the stem to within 0.1" of the bar clamp, and fabricated and installed the cable housing stop. It is a press-fit 7mm rod. I press-fit it and then bored with a tiny end mill and drilled the tiny hole for the front brake cable. Also drilled and tapped the hole for the bell.
And I did a test-fit. It fits well!
I'm done with major machining steps on this, and ready to give it a nice finish-filing and polish!
The weird bolts I used do not have slots yet. They are just hex head bolts I turned into Herse-shaped heads on the lathe. They're stainless, so not true to original. I may find a better solution (ideally pre-slotted steel screws) that I can send to be chromed along with the rest of the hardware.