HEI in a Mopar?

I'm not so sure about that. Maybe people who did that are the reason we read of Mopar ECU's with melted epoxy filler running down the inner fender. The early ECU's (5-pin) required a 5 ohm ballast on the ECU supply pin. Those were the "dual ballast" design. Later ones (4-pin) operated from full 12 V, but I think they still needed a ballasted coil to protect both the ECU and coil. I have had several Holley XR700 electronic ignitions, which was designed a little later than the Mopar ECU, and the manual says to keep the ballast in the system. Their XR3000 does not require a ballast, but was designed for "racing only".

if you look at a 4 pin ECU diagram you will see the ballast wires do not feed the ECU they come straight from 12 volt switched and one branches off to feed the ballast but its not on the resistor side of it