I really think the counter weight on the crank shaft takes care of the piston,as long as the MFG has done a reasonable job of balancing the rotating assembly, one should never have to mess that headache.

My opinion on prob balancing thats it not AS necessary as it once was, prop MFG also benefited for the computer controlled CNC machine process and if you really wanted a perfectly balanced prop you would have to do it under a glass box as you breath, AC/Furnace and natural convection currents in a room would influence your results.