Spark plug gap for Pertronix ignition?

I have converted the points ignition on 70 Cuda 340 to Pertronix electronic. I have been running Champion RN9Y plugs at .030 gap. Is there a better proven plug and/or gap for use with the Pertronix. Pertronix instruction said must use plug wires for electronic ignition so changed that over. Runs Ok but hard starting. Does anyone have recommendation to make better?