you'll need to do a squish test.  There's probably a thread around here that has pics to go with the explanation.

1.  Get some .062 solder. 
2.  Remove the head from the cylinder. 
3.  Roll the engine over so the piston is on the upward stroke just before TDC. 
4.  Cut a piece of solder and lay across the piston perpendicular to the intake and exhaust ports.  Make sure the solder is touching the cylinder walls on both sides. 
5.  Put the head back on the cylinder. 
6.  GENTLY roll the engine over TDC.  BE CAREFUL to not go too far so that the solder falls down to the crank.
7.  Remove the head and grab the solder.
8.  Mic the ends of the solder that are squished.  You want to be .045 to .060 -ish.  I like to be in the .05's.  Any adjustments need to be made at the base gasket.  Cometic sells gaskets at any thickness.  For example, if you're squish measures at .04, order a .015 or .02 gasket from cometic.  That will put you in the .05's -gaskets squish down a bit when you torque the cylinder studs.

Hope this helps