This issue was a pain in the @$$ to me. Couldn't figure it out, thank god for a close friend of mine with good eyes!
My motor would just shut off randomly, basically like if you were to just turn the key off. It was very temperamental, sometime would run for 10 mins, sometimes for a few seconds. Looooooooong story short, it ended up being the module in the distributor had a loose connection. Where the male and female ends meet, the female end was loose. Took a set of needle nose pliers and tightened them up. So far, have had no issues.
Thought i would mention my issue with that for the next HEI sucker that may run into this.