I ran 10.0 comp in my old 440 with 906 heads and quench as I used the KB quench pad pistons. I ran the MP .557 cam because as we all know the cam has alot to do with it also. I ran 38 total timing using 92 pump and had no problem as I had no ping at all. In fact the eng is still running in a Duster as I ran it from 2006 until 2011 in my 63. I had no vacum advance on it as my dist is a race type and has no vacum advance on it. You could run 10.5 with iron heads if it is built right being the cam , cyl pressure and so on. Myself I would not push that much on todays gas if I was building an iron headed street car. I felt I was pushing it at 10.0. You would be better around 9.5 as many said here because if the build is not just right for pump you can still get away with it much easier at 9.5 comp. Ron