definitely check your timing flat tops with 64 cc heads should get ya 10:1 er so maybe 10.5:1. witch is ok for premium pump gas assuming its tuned properly, 34-36 degrees of total timing is about normal for a sbc......
make sure your not leaning it out too much, an improper air fuel mixture will cause pre ignition as well....
if none of this works you could also try retarding your cam timing some to help reduce cylinder pressure and your dynamic compression ratio....
your dynamic compression needs to be about 8:1 with iron heads, if you know your cam specs and such there are calculators online to help you figure out your dynamic compression ratio......
dynamic compression should be around 8:1 for pump gas and static compression around 10:1.....
also check your quench height or "squish" witch is the distance from tdc to the top of the deck and your gasket thickness added together, a large quench area will also make it more prone to pre ignition .060 is about the max quench height they say you should run on a hi perf engine
hope this helps
-logan