318 no start after sitting

I think you already found the problem -- junk, dirt, moisture on the circuit board of the dist. I tried to tell you before, I BELIEVE that distributor is magnetic pickup just like a Mopar. You should be able (I believe) to yank the board out of the MSD dist. and trigger the magnetic input of the MSD 6 directly.

What you REALLY have with the MSD 6 is TWO ignition systems---the junk in the dist, and the MSD 6.