Fair chance you'll need premium to keep it from pinging.
What you want to avoid is backing the timing off from the best power timing to stop the pinging. This is because lowering the timing kills the power and mileage.
The 256 Comp cam has a relatively early intake valve closing (IC) point (55° ABDC @ 0.006" lift). What that means to you is the static compression ratio (SCR) that I estimated to be about 9.6:1 on your last thread will make the dynamic compression ratio (DCR) to be about 8.25:1. This
page (written by techinspector1) will give you an idea of what CR is needed for different durations.
Until you know the exact
static compression ratio as well as the quench
distance (and that brings you back to CC'ing the combustion chambers and measuring how far down the hole your piston sits and the dish volume), this is a ballpark guess ONLY!!! To use my figures w/o checking my math and using the correct SCR might cost you an engine or at the very least cause you to tear it back down to correct the CR or to run race gas or to retard the total timing.
Online Calculators (there are others):
• SCR calculator
• Wallace Racing DCR calculator
• Kelly DCR calculator
• KB/Silvolite DCR calculator
You also need to use a vacuum advance and set the ignition timing advance curve
up correctly. There are MANY threads on this. After reading up on it if you still have questions, just ask and we'll try to sort it out for you. But first you need to research it for yo'self.