Just my .02.... I agree with Mr. Tech and my gut instinct is that your balancer is off a little. When you can retard back to 0 DEG and your pre-ignition goes away........my first place to look, if it were my engine, is establishing true TDC.
You could try the afore-mentioned stuff but I would want to be sure my timing marks are dead on. Check the weights on the advance and make sure they spring back freely.
I hate to even ask this but you do have the vacuum advance disconnected and plugged when checking the timing right??