how much to mill?

i need to know how much to mill from my cylinder head to get a 9.25-9.5:1 compression ratio. the head was pulled from a junked car and my machine shop says that it has been surfaced, but we cant tell if it's been milled. i cc'ed the chambers and the are 58cc each. i know that 0.1" can be taken of, but dont know if some is already gone. how many cc's can i expect to lose per 0.01:? i'll be running mopar's mild competition cam, and this will be a street car.
thanks for any help!