Factory specs are that all pistons and rods should be within 10 grams of each
other (I guess that is MINIMUM acceptable).  But the closer you can get
everything the better......

Pistons have little lugs cast inside them that are designed to be removed or
ground for balancing purposes.  If you actually remove all of these lugs, and
you are only just within 10 g then that is what you have to live with - no
other part of the piston should be attacked......

The ability to 'balance' pistons etc to a certain degree does come back to
the quality of the set you buy - greater care in the casting and post-casting
maching process results in components with less variance in weight.....(and
ergo the best chance of a close balance)...

BTW this is only one part of the balancing process - the distribution of
weight is also important - you can statically balance rods and pistons (which
is a process like getting the right weight for equilibrium on a see-saw),
easiest to go to an expert to get the crank dynamically balanced.  There is
no real need to go through this second process for a 'stock' motor....

Later

Rob K.