"It is MUCH more important
to balance rotating parts than reciprocating."


I challenge that. Acceleration of a mass (or mass error) creates the
same dynamic force whether in a rotating motion or in moving in only a
translational motion. The only difference is that the force direction
is changing vs just reciprocating.

One gram may be overly accurate but it is something that is easily
achieved. I recall a Continental paper that said though that they
deliberately built up an engine with one pound (!) heavier piston & it
ran "satisfactorily".

Yeah, I'll bet......!