Petronix thoughts

The original (Ignitor I) is similar to the Mopar ECU and still needs a ballast resistor (I think). I would run that instead of the orange box, since those are problematic. Sell that to someone already wired for it. I plan that for the orange box I got before I changed my mind. Ignitor II is better and allows you to lose the ballast and run a better E-core coil. Ignitor III adds multi-spark.

Other options - new distributor w/ integral HEI module ($45 ebay "ready to run"), GM 8-pin HEI module w/ GM coil but requires an E-distributor.

All these little modules work by the power of semiconductors. They can be much smaller than the orange box because they are more efficient so don't generate as much waste heat and require large heat sinks. If you want more punch, checkout the MSD Stacker (original model), which you can add in parallel.