Now you have to do the homework to calculate your compression ratio. This is basically a comparison of the amount of space in the cylinder/combustion chamber when the piston is at it's lowest point (bottom-dead-center, or BDC) and when the piston is at it's highest point (top-dead-center, or TDC).
It's usually easiest to calculate this separately, meaning the volume of the cylinder can be determined alone, then calculate the volume of the compressed head gasket, combustion chamber in the head, and any dish or valve relief in the piston.
Once you've got all of your dimensions, calculate the ratio of the volume at BDC vs. TDC and this will be your compression ratio. You can then determine what the TDC number should be to acquire your target compression ratio. The TDC target number will be smaller, which means you'll want to take some of the volume out of your combustion chamber.
Every slice you take off the bottom of your cylinder head makes your combustion chamber smaller. Typically, I measure the volume after every .010-inch slice removed from the head. Because the shape of the combustion chamber is tapered, you'll remove a little less from the chamber every time. Once you've reached your target chamber volume, you'll know your target compression ratio has been reached. You've got pleny of clearance to the piston, and I'd guess you'll remove .040-.060 or so from the head to reach your target number, which should be about 9.6:1 for pump gas.
Once you've got the heads shaved, use a file to cut the sharp edge all the way around each combustion chamber, bolt hole, and water passage on the bottom of the head. Sharp edges are where cracks begin. You don't have to massage these edges round (doing so may affect their ability to seal) but just take the sharp edge off.
Clean the head completely before reassembly, as the shaving process creates plenty of shavings and grit, which will find their way all over an into your heads. After a good cleaning, reassemble the heads and they should be ready to reinstall.
Once the heads are reinstalled, you'll need to reset the valve clearances. If you're running hydraulic lifters, this is as easy as adding one half turn past 'snug' with snug being the point where the pushrod no longer turns freely.
I hope this helps...
~SP~
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