Electronic ignition upgrade.

The HEI upgrade is a very good upgrade for a number of reasons. You should use an E core coil [ such as MSD #8207 or similar ] to get the best out of it, as they produce more spark energy.
- HEI has variable dwell, Chrys ECU doesn't. Important for high-er rpm operation
- variable dwell keeps the coil cooler.
- any ign system that eliminates the bal res, all else being equal, will produce more spark energy
- run with 0.060" plug gaps with HEI; you cannot do that with Chrys ECU, it is not powerful enough...