- Presumeably these would be of the GX160 or GX200 type (ref. "Considerations Concerning the Fitting of (New) Pistons...").
It is not immediately obvious that the gudgeon pin is located slightly off-centre to the piston's central axis: as near as I can measure it, this off-centredness is 1.1 mm., see diagram below, in the direction of the cast-in arowhead in the piston's crown.
I have no idea how accurately the c/l's of the cylinder bores intersect the c/l of the crankshaft: the tolerance-chains here are considerable. But, whatever the accuracy of these alignments, it would yet be advisable for the starboard (=RH) piston to be fitted with its arrowhead pointing upward, and the port (=LH) piston's arrowhead pointing downward, as this would tend to reduce a piston's side-thrust against its cylinder wall on its power stroke. And less thrust means less friction, means less power loss.
How important might the foregoing be? Probably not very, but it could do no harm to heed it.
Another matter may concern the internal gudgeon pin bosses in these pistons.
It is well known that conrod centrelines are not central to the cylinder bores, due to the basic dimensions of crankshaft and crankcase: but very long tolerance-chains can also affect this off-centredness significantly. (It is in partial compensation for this, that overlength small-end bushes are set asymmetrically in the small-end eyes). In extreme cases of off-centredness, however, it could mean that a piston's internal gudgeon pin boss would need to be shaved back a little, to provide clearance with the small-end bush.