I refined the design a bit to make it more sturdy and parts less breakable, and I'm happy with the result.

I'm definitely ok with a 1mm dia mast as well--it looks sufficiently "thin" to me, especially at three feet. Besides: I need to fit at least two strands of magnet wire down the mast (one + red, one + green) so it needs some room.
I needed to test the head design for installing the 0201 LEDs; The first design was endlessly fussy (aggitatin')... the second iteration made installation of the LEDs easier, by threading them from the front; They were secured with a drop of PVA. To wire the signal with concealed wires, I planned to cut a notch in the front of the mast behind the signal head and run both positive wires down it, then solder the negative wires to the (brass) mast. Here's the test with the regular warm white color LEDs:

PRR or N&W PLs anyone.. ? Since I need B&O color lights, my idea was to make "lenses" with clear paint. I got some Monument Hobbies PRO Acryl Transparent Red and Green and painted a "lens" in the signal head. Here's the first test:

I am actually very happy with the colors; Here's a test with the green paint and head/mast painted black:
So far so good, next up should be a "full" test with all the details added. I have 4 of these to do and one practice and 4 extras are my idea. I also need to dig out my smaller tip for the soldering iron. The current one is a 2-3mm wide spade.