Hi Folks,
Real 340 cranks have a deep line cut across the second counter-balance that all the other S/B steel cranks don't have.
The undrilled rod throws is also a big giveaway too!
Any good shop will re-balance a steel crank for the heavy rods.
Most heavy rods S/B (and B/B) can be reworked on the beams and end weights to get them real close to the stock 318 rod wieghts anyways (and LY rod).
PJ