This engine has a carburetor with electric advance, the ECM in your case would be part of the "early fuel evaporation" (EFE) system, basically governing when to open/close the exhaust for exhaust gas recirculation. You can read about how that system works here: (https://www.autozone.com/repairguides/GM-Chevy-Mid-Size-Cars-1964-1988-Repair-Guide/Gasoline-Engine-Emission-Controls/Early-Fuel-Evaporation-EFE-System/_/P-0900c152800515ab). The ECM is behind the driver-side kick panel, should be able to follow the cable to it. I'm pretty certain this is the module you are referring to. There is another module that is part of the HEI distributor but that is not referred to as an ECM.
1 people found this helpful.