Here's the general idea. The trick will be to diffuse the light enough that it doesn't look like they are LEDs. The other trick will be to separate the high and low intensity "filaments" on the tail / brake light so they don't feed back into the system. That's easily done with some regular signal diodes, and two different resistors. With both resistors running in parallel, I'll set their combined resistance at the maximum current of the LEDs. With only one running, I'll see what percentage of max current still gives a decent output for the tail light "filament" circuit.
The running lamp bulb in the headlight should be even easier. I can just use some white LEDs and pile them into the bayonet base of a dead lamp. Diffusing this lamp will probably prove to be more difficult since there's nothing to hide the fabricated LED lamp assembly in the big headlamp housing. Maybe a piece of plastic diffuser or reflector from something else will work.
I did sacrifice an ultra-bright LED that I had in my junk box from an old project to prove a concept. Most LEDs have a rather narrow view angle. I took the file to the lens of one of these LEDs and ground it flat. Then I used some fine emory paper and polished it up. I'll have to refine the technique, but essentially it works. It diffuses the light into a wider area, rather than focusing it into a beam. I did get a weird halo effect, but I think I just need to polish the edges a little more.
I don't plan to run the bike in the dark if at all possible, so If I can just reliably run the running lamp circuit without the main beam I should be fine. The main headlamp is a HUGE 30w draw on the dynamo, and it just doesn't keep up.
The running light in the head lamp was easy. 6 Ultra-Bright White LED's soldered into a bayonet lamp base. The rear tail light lamp was a little more challenging, per the above diagram.
Dang! that's BRIGHT!
Both these replacement bulbs LED assemblies draw less than half an amp and put out MORE light than the original incandescent bulbs.