impossible your either talking that for the piston to go up to a certain height and stop so either the piston diameter is too small or too big or its the sleeve pinch causing the piston roelof there is no way from piston to piston of sleeve to sleeve there can be such a measurable difference just cant happen, then what if u say is true think of all the other things that could be wrong such as where the bearings sit the opening could be bigger and the bearing would fit looser or tighter on different blocks, carb openings would be different motor to motor cause if what u say is true then it don't just apply to piston and sleeves every aspect of the motor would be different that is impossible!! no way....
also there is no way they set aside the better ones for the gold head for what reason the gold head is not sold as a better motor or sold as a modified motor it just don't add up.
bottom line some motors are just cut sharper like I said and certain ones get the luck of having the sharper pieces put toghter...
You do not have an understanding of the basic engineering that is used to manufacture the PS sets. The taper is deliberate due to the temperature gradient from the top of the sleeve to the bottom and it is GROUND into the hard chrome, not cut. The small tolerances required and the process require matching of piston to sleeve and as Roelof says, sometimes the variables just stack up better. Sometimes by accident but usually deliberately. Even the variations from batch to batch in the alloy of the brass base material and piston aluminium has an effect.