If you have a real F-Body SuperSix distributor it should have the 9R governor. This will limit advance to 18* total. This will allow you to sit initial to 12* BTDC. I believe the guy on .org is still selling his spring kit. His kit includes a crude chart on how the springs works.
Now it is trial and error to figure out what works for your combination. I suggest a dial-back timing light and a chart to map how the spring set works for your combination.
