Hi Tom.
A few comments on your schematic in post #6.
1. You NEED to put a resistor in series with the pushbutton. The way you have it drawn, when the pushbutton closes you will be applying 6V across the base-emitter junction of the "51A" transistor. This will cause excessive current to flow in the transistor and the essential magic smoke will escape from it. The value is not critical; 10k will do nicely.
At the same time you could change the 360k base-emitter resistor to 10k as well, and move the transistor so it sits just above the "66F" transistor in the diagram and connects directly to the 6V rail with its emitter at the top. This is a more common way to draw a circuit section like that one.
2. I would not connect an LED the way you show, mainly because it will draw some current and will cramp the flyback voltage at the collector somewhat.
3. I recommend connecting some kind of overvoltage protection network in place of the LED. The peak flyback voltage at the collector will be limited by the secondary voltage and the spark gap, but if that becomes disconnected, the collector voltage might shoot up so high that the transistor could be damaged.
A typical suppression circuit would be a high-speed high-voltage diode with its anode to the collector and its cathode connected through a resistor (330 ohms or so) to a zener diode (cathode end) with a capacitor (e.g. 10 nF) in parallel with it, returned to the +6V rail.
The flyback pulses pass through the diode and charge up the capacitor, but the voltage across the capacitor is clamped by the zener diode, so the flyback voltage can never exceed the zener voltage. You choose the zener voltage so it's a bit less than the rated maximum Vce of the transistor. You may want or need to use several zeners in series to get the required voltage; also, the zeners should have low leakage current, as any leakage current represents wasted energy.
Edit: Another option is, as Duke suggested, to put a low-value capacitor directly across the primary of the coil. This forms a parallel L-C tuned circuit which produces a flyback pulse with a controlled shape. This capacitor corresponds to the "condenser" used in engines from (I guess) the mid-1900s. I don't know whether older engines used a "condenser" or not.
4. I'm pretty sure you have the primary connections on the coil connected the wrong way round. The tap (marked WH and BK) should connect to the transistor's collector, and the bottom end (which you show connected to the core) should connect to the +6V rail.
5. You should investigate the duty cycle of your drive waveform. Generally flyback transformers are operated with a wide current pulse and a relatively narrow flyback time, because the flyback voltage is so much higher than the voltage applied while the coil is "charging" (charging up its magnetic field).
Your design currently has a duty cycle of around 58% at the 555 output and therefore 42% at the coil driver transistor's base. When the transistor turns OFF, the flyback pulse will decay relatively quickly, and the remainder of the 58% of the cycle time will be wasted. I think you should have at least 90% duty cycle at the base of the coil driver transistor. There are many ways to achieve this. Let me know if you want suggestions.
6. What's the operating frequency of your 555? A 0.1 µF capacitor with those resistor values is going to give a relatively low frequency...
is; from what I have read, and believe to know, the coil field collapsing produces a return voltage spike (actually a few spikes) back into the NTE261 transistor. One is supposed to put a diode across a "coil" to prevent this, but when I do the circuit fails. The original “web found” circuit also did not have a diode, but it did have a 330 ohm resistor and LED from the collector to +6v. Would that path through the LED be enough to protect the NTE261? – no it appears spikes are still present after testing.
