What CR are you looking for? If you are running the stock cam, (VERY short), I would not cut more than to remove the step from the quench area. If you are running a big cam, you may be able to cut more, (more CR), but would need to check valve to piston clearance. With the stock cam, I doubt that would be an issue, (there is a lot of room there). I would also open up the chamber around the valves by the cylinder walls. I would make it so the chamber was flush with the cylinder walls right by the valves. I know this will reduce the CR, but it adds air flow. You can also make it a compound radius, not only matching the radius of the cylinder wall, but also making a radius from the chamber roof to the deck surface. This will give the least reduction in CR, and the most improvement in air flow.
Don't forget to check your pushrod length when you are done. Cutting the heads will make the pushrods too long, and throw off valve train geometry.
Tom
