there are alot of ways to find compression ratios. You need to know some things first though. Most heads gives you head chamber volume and pistons do to (the number on your piston is the volume in cubic centimeters) head gasket specs: most head gasket co. list specs thicker head gaskets and bigger bores gives lower compression ratios.
go into these links to find a formula that will calculate your compression ratio with the above info.
www.mindspring.com/~steveflyer/compression.htm
www.smokemup.com/utilities/calc/compression.raatio.cfm
scott