You may have a better idea when you open it up. With a small pry bar push weights out until you see the heavy spring take up some slack. Is right at the begining, at the near the limit or something in between?
Thanks for the suggestion. I took it out and test-reassembled with just the heavy loop spring, since I can't get the superlight spring until tomorrow. Using the FBO limiter plate as a guide, it seems to hit the loop and the plate more or less simultaneously on the 14 degree slot. I think that will probably work :)
So if I set the initial to 16 for easy starting, it will idle at 30, and slowly advance on the heavy spring thereafter. I will still have to modify the longest slot on the FBO plate (18), since 16+18 would only allow 34 max. which at high RPM would be less due to box delay. Will have to determine just how much less by actual timing light reading. I need a limit at roughly 20 degrees...
The other option is to eliminate the limiter plate, and shorten the distributor slots instead (stock range will allow too much total advance when starting at 16). I think I'll file on the limiter plate instead :)