Yes, I believe that the SDS coils are GM or equivalent.
Regarding carbon fouled plugs, I think you may have to replace them. I don't think the gap resolved anything from what I recall, but that was lots of years ago - mid 80's.
I'm really clued-out by your discussion about your coils. I understand what's going on, but I had no idea that MS offered you the ability to mess with such variables.
Does your engine run clean to 7000 at very light load without any boost?