R3: The issue isn't RPM unless you are relating to 'flexible or
non-flexible rotors'
Typically Auto cranks are balanced by drilling the counterweights a
little
deeper or what ever.
I can't say about Franklins, but Lycomings and Continentals do not have

counterweight molding in
the casting because the arrangement is a 'balanced' engine in the 1`st
order
by design.


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Look close at the Lyc / Cont cranks and you will see balance marks on
the rod throw end. As you have pointed out they don't have counter
weights so thats the only logical place to correct a large imbalance
that happens during the crank forging process.