Thanks Rhys, I was doing just as you suggested when you were most likely typing that post. I used a remote camera probe to discover gunk, and used a pick to clean out the head enough to make adjustments.

On to the interesting stuff:

Before any adjustments, the dwell was about 55 deg. I managed to get it down to around 45 deg after adjustment, although it jumps around between 40-48 deg.

Just as a test, I turned it to both extremes to see what would happen. Going higher to 60+ deg produced more of the same symptoms, chugging and rough running, but steady RPM. Going lower got it smoother to a point, but then around 30 deg, it began surging until it died. However, it was clear to me that at lower degrees, it was much smoother running, it just won't remain steady.

The problem I have is that it is still equally rough at 45 deg, and won't really idle below 1000 RPM. Going lower than 45 helps, but it begins surging uncontrollably.

I also note now that I can screw the idle screw all the way in and lower the idle to around 800 RPM, but can't completely kill it. Is my idle control valve making up the difference?