MP electronic ignition conversion kit

What is the difference between the new ballast they supply with the kit and the old ballast on the points type cars.

I'm converting this 72 Dart from slant 6 and points to V8 and electronic ignition. I have an orange box and wiring harness. Thinking about using those two items along with a factory stock 1974 318 electronic distributor. Don't have the ballast can I get one from local auto parts store? Part number?