FRANK66, if your cam is unknown then i would start with the spring that were in the distributor,run the engine to 3,000 rpm set the timing to 38 degrees with a adjustable timing light or timing tape on balancer and then look at your base timing should be 8 to 14 derees.think if your running the car it will be 2500 to 3000 rpm over 30 mph anyway (depending on your gears)if the spring rate is real bad you'll get a stumble or flat spot on accel.My friend runs a 502 with no vacuum or mech. advance,just set at 38 degrees all the time and it runs killer-only loads up if idle for 10 to 15 min.This would be no problem if you have a vacuum and mech. advance.I would set it to 38 with the vacuum and mech advance connected and go for a run to test.-MIKE