WOW! Guys, we really need to go back to basic electricity and electronics. What does a ballast resistor do? Good question, glad you asked. It was used in the old days because points would ground out the coil for a long time at idle, and less time as RPMs increased.
Now for the reflection on basic electricity. An ignition coil is an inductor. More specifically, a step-up transformer (which is inductive). Looking at it in the pico-second resolution, when you have battery voltage going to one end of the inductor (coil +), and the points ground out the other end (coil -), the coil begins to convert electrical energy into a magnetic field. At first, there is absolutely no current flowing. As this field builds, current increases. There is a point where the magnetic field is as strong is it will ever get at battery voltage. When this happens, the windings inside the primary side of the coil flow current just like plain 'ole wire.
How long do you need to pulse the coil? This is your Dwell. In the old days, you adjusted Dwell by gapping the points. Fact is, the actual activation time varied with RPM. Think in terms of milliseconds here. Low idle delivered a long dwell time. As RPM increased, actual dwell time (in milliseconds) reduced.
Let's see how a ballast resistor could save the day. Ballast resistors increase resistance when they get hotter. Higher temperature, higher resistance. If you have current flowing through even a straight wire, it can get hot. (Ever crank and crank an engine that didn't want to start and touch the battery cables??) When the points would deliver way more dwell than the coil could handle without burning up, the ballast resistor would lower the voltage so the coil survived. Increased resistance "throttled" current, and thus voltage.
With all of that background, your goal is to deliver proper spark to the plugs to fire the air/fuel mix. This is a function of your chosen ignition system. So I ask you to question this: WHAT DOES YOUR IGNITION SYSTEM HAVE TO DO WITH THE ENGINE BUILD AS LONG AS YOU CAN FIRE THE CHARGE AT THE RIGHT TIME?!?!?!?
Just use a tried and true ignition system and don't put too much thought into your original question. Just my educated and professional opinion. Hope it helps.
