I had a chance to look into this today. Just wanted to thank Rapid Robert for the chart he posted. I used two stock light springs and ended up just what i wanted on the first try. This distributor also had a short slot .380 "in the plate". So with my 18 initial, I ended up at 35 degrees right at 3000 RPM.

Dr. Charles... I can tell you that with what I used, I still had 18 degrees at 1500 RPM. The stock setup i was up to 21 at 1500 RPM. It would seem that the stock heavy spring with the long loop lets the weights take off quicker (advance), but then hold it back later. The two stock light springs hold the weights a little bit, but then advance quicker... Hope this helps