...Auto guys will then make up a bobweight of nuts and bolts
... equal to the rotating part which they add to the crank throws and that is
... then spun on a dynamic balance machine. ...

Yes. Thats true for V8's or V6, etc. But not needed for opposing cyl
engines.

.. I can't say about Franklins, but Lycomings and Continentals do not have
... counterweight molding in the casting

Its the same for the Franklin - its an opposing flat 6. Opposing flats
are inherently easier to balance.