[Big hammer]

Chris! Sounds ( or no sounds) like what your doing is good! Pulling your spark plugs and reading them will tell all. What causes pre ignition, a hot glowing spark plug, carbon in the combustion chamber, over rich or very lean fuel air mixture, over heated engine.
Go for a ride and get it warmed up, cruise at your steady cruise speed, push the clutch in and shut off the engine, when your stopped pull the plugs and read them. There's many places to see pictures of what your plugs should look like.
An advantage using a aluminum head is, aluminum dissipates heat faster than a iron head :-)