Clamping the octal tube into the Sherline let me set the XY=0 origin to the center of the base with the laser dot (visible near the front):
Find the edges, touch off the half the 32.2 mm diameter, then align the drill at XY=0 directly over the exposed evacuation tip:
Make a very shallow cut to verify the alignment:
Just inside the scuffed ring from the drill, you can see the fractured ring where the original one-piece Bakelite spigot / key / post broke off.
Then extract the drill from the chuck, file more relief behind the cutting edges so they actually cut, re-chuck, and continue the mission:
Pick a nice Bakelite ring out of the drill:
And eventually you can see all the way to the glass envelope:
The (knockoff) Neopixel LED sits directly below the evacuation tip and is about the same diameter, so much of that enlarged opening will be in shadow. Despite that, the tube does seem noticeably brighter:
Drilling that tube was so harrowing that I can’t imagine similar surgery on an intact octal base.
Perhaps just slicing off the tip of the Bakelite spigot and gluing a single very bright red/orange LED in place, rather using than a (knockoff) Neopixel a few millimeters away, will suffice.
Or just give up, top-light these tubes, and move on?