Oh man, where do I start? Rather than getting into the complex makings and materials of head gaskets, let's just talk about thickness and bore. The Fel-Pro head gaskets have great descriptions of what they are and will oftentimes give you a compressed thickness and gasket bore size. The Fel-Pro 1044 head gasket has a 4.200 bore to clear most stock/bored SBC pistons and features a 0.051 compressed height. A thinner Fel-Pro head gasket 1094, similar to this one, has a 0.015 thickness with 4.100 bore and will increase compression because of the decreased space between the combustion chamber and piston (squish area).
Squish is referring to how much space the piston has before making contact with the top of the head and combustion chamber. It is named that because the head's combustion chamber is designed to compress the incoming combustion charge at the last moment and squish the charge toward the spark plug. This squish effect gives the charge turbulence and in effect gives a more complete combustion and burn. A target of 0.041 squish is the goal for our 383 build.
Like the squish area, the quench area is the distance in relation to the piston and the top of the flat part of the head. Quench is referred to as a way to reduce the compressed mixture temperature between the piston and the cylinder heads. Both are very similar and can often interchange depending on whom you are talking to. Ideal quench and squish on a small-block is .035 to .045 depending on the application. Believe it or not, increasing the piston to head squish/quench clearance too much can increase ping or detonation.