Any Pertronix experts here?

Using a coil with high pri resistance results in less spark energy, all else being equal. If the module will work with a coil that has 0.6 ohm pri resistance, I would find an E core that has ~0.6 ohm pri. They are more efficient than canister coils. There is a reason GM was able to run 0.080" plug gaps [ on some engines ] with a 0.6 ohm E core coil.