Which HEI modules have you tried and do you have your module mounted on a heat sink with a coating of heat transfer grease? Is the coil in the proper resistance range for the HEI ignition? This module is highly rated, this will probably be the setup I use when my orange box gives up the ghost.
Davis Unified Ignition Dyna-Modules 000222 Mounted on this
ACDelco Ignition Module Heat Sinks 10474610 at the usual location for the factory ballast resistor.
