[Lynn Eades]

Phillip, The conduit threads are just that. The answer is to find an old electrician with a set of B.S.Conduit dies. I found a set over here on Trademe quite easily.
3/4" o.d. is the same tpi as UNF (3/4"x 16) but i'm guessing your wanting to run a thread on 1" conduit which is also 16tpi and is specific to B.S. Conduit thread.
The resistor should be fine as long as you have continuity.
If you use an original (Ford) coil, they are notorious for failing when hot. The insulation (even in a nos one) will likely have deteriorated.
They can be rebuilt in the U.S. if you are that keen.
Basically how the system works is that the Ford coil is a 4.5 volt coil.
When you first turn on the key 6 volts goes through the cold resistor to the coil.
This gives the starting h.t.voltage a boost while the battery is under load from the starter. As the resistor heats up the voltage to the coil drops down to the 4.5 volts.
If you use the Ford coil without the resistor, it will eventually burn out.
If you use a std 6 volt or indeed a 12 volt coil, bypass the resistor.

The lighting circuit breaker: If you get a short in any of the light wiring, it will rattle away (noisily) and hopefully your lights still sort of go. Basically an abnormally high current draw will open circuit the relay. It however shuts again very quickly, suppling power to the lights again(momentarily)
When this happens, turn 'em off. It needs fixing.
If power flows through it and you can physically open the points (Which probably need a gentle clean)and they close again (spring) then it will probably work?