The later Sherpa engine have drilled holes in the piston an "deep vertical grooves" for additional flush, so the crankcase volume is importand.
To determine where to drill, ... was wicked, (old piston left new one right), as the location of the grooves can
vary between the cylinders the holes where made by hand to the specific cylinder. (the shown used piston is the original one with around 1600km, the new one is NOS with first excess). By the way the piston pin is not centered as the ultra short stroke in combination with 85mm bore tends to nod/wobbel to avoid this the pin axis is moved some mm.