I believe Hughes told you that because the aluminum head can run about 1 point higher in comp to be equal with and iron head. So if you run 10.5 with the 452 aluminum head its like 9.5 with the cast iron head. I can tell you we milled the Eddy heads on my sons 400 .040 to get 10.8 comp. It does not have good quench but runs fine on 92 or 92 pump and it has no fitting problems as we milled the intake side .040 also.

Sure you can run the comp at 9.5 but you will have a little better performance if you up the aluminum headed eng to 10.5. You will just loose a tad of power at 9.5. That said I run 10.6 in my aluminum headed 493 and it does have quench and runs great on 92 pump. Ron