1970 340 ignition module

Hello, I have a 1970 dart 340 4spd car. I bought a new wiring harness for it from classic industries for the updated electronic ignition. The car has no ignition module and the 2 connection ballister not the 4 prong one. Runs fine! I have a electronic distributor I'm installing My question is...So the wiring harness connection that plugs into module is a 5 pin, what pin module do I need? Will 4 pin module work? And classic industries states I must use the 4 prong ballister...any info would be great and reasons why. Thanks guys