3.31 and 3.58 are the stroke difference in a 340 and a 360, take difference (.27) , divide by 2 (.135) and you have a ballpark compression height disparity between the 2 pistons. Eg, a +.040 360 piston is going to have a shorter compression height by .135 (to compensate for the longer stroke) than a low comp 340 piston to have the same compression in the same bore with the same head. When you start adding compression height to a piston, your compression goes up rapidly. You get the idea.