Kb356 pistons

If you were to use a head gasket with a 0.020" compressed thickness or machined the heads to get the chambers to 60cc you would be just over 10:1.

The dish volume in those pistons is 23.5 cc, a typical Fel-Pro head gasket has a 4.180 bore and a compressed thickness of 0.039 and the magnum heads have a chamber volume of approx 64cc.

Here is a slick calculator that you can play around with different specs to work out the compression ratio you want.

http://www.csgnetwork.com/compcalc.html