Hi Rocker:
Your HEI problems sound very similar to mine I had about 10 years ago on my 1976 V8 HEI. I followed my factory service manual troubleshooting for the unit and it diagnosed the coil and module as bad at two separate troubleshooting occasions. After replacing both of these and everything seeming ok for a short period of time, the starting problems occurred shortly after. Replacing both these parts repeatedly after following the troubleshooting guide, the whole process was repeated...still intermittent starting problems. So I finally decided that the only old electrical part left in the HEI system was the pick-up coil at the base of the distributor...I could not find this as a spare part and so I just bought a complete new HEI distributor with the pick-up coil. This solved the problem and so I think the pick-up coil was intermittent or bad...I followed the GM troubleshooting guide very closely and it did not lead me to this little coil.
Hope this helps,
Henry