The ignition module is the key part of this upgrade. My first choice would be to visit your local wrecking yard and look for a 1974 to 1990 GM vehicle with an OEM 4-pin ignition module (AC Delco D1906 or equivalent). I would grab the wiring harness and connectors from the distributor to simplify the conversion work and to have a better appearance.
HEI Heat Sink
The HEI module generates a lot of heat that must be dissipated in order for the module to have long life. The large cap HEI distributors just used the distributor body as the heat sink. The PN 10474610 heat sink was used on later computer-controlled ignition systems but will work with the 4-pin module when modified with some new holes. You need to put a heat sink thermal compound between the HEI module and its heat sink to ensure that the heat transfers into the heat sink.
|ACDelco 10474610 GM OEM Ignition Heat Sink||Heat Sink Thermal Compound|