Ballast resistor wiring

Righty said
So in my photo would you be saying that J2B and J3 are joined in the connector and still effectively running from the ignition switch to the coil and are still an active part of the start ignition circuit, with power coming from J1 via either R6 or A1A?

I don't think the original J3 is providing power to the ignition during start because somehow the ECU needs to get power.

Yes A1A provides power battery power during start.
Then R6 provides the power when the engine is running.

Righty said
And then J2 / J2a (as its a 69 model) is bringing power to the 4 pin resistor and feeding the coil via the red wire labelled coil in my photo?

That what it looks like to me as well. The top resistor should 0.5 ohms

Righty said
Looking at the coil it has 2 wires in to positive - the pinkish wire from the 4 pin resistor that I labelled Coil and another red wire, perhaps this is a continuation of J2B / J3? It's my only explaination, they disappear into a mess ofwires in electrical tape and the red wire comes out of it further along.

That is odd.

Righty said
The black and yellow wire to the negative on the coil I think does run to the top pin on the ECU as shown in your diagram, there is a second wire (red) from the negative on the coil which I believe might have been to an aftermarket tachometer.

That would make sense.