Aluminum vs Iron compression on pump gas

I have stock magnum heads (measured at 64 cc) and zero deck flat tops for 10.6:1 compression and 190 psi of cranking pressure. I run a 224/230 @ 0.050" cam, the quench distance is 0.039". The magnum heads are a much more efficient so they don't require as much total timing, I run 33 with 17 initial all in at 2500 rpm.

I run 89 octane on this setup and have run 87 in a pinch but it will detonate under 3000 rpm if you are not careful.