balanced??

Cast crank 340's had weight welded on the converter, but most obvious was the balancer/damper which would have a raised ring with counterweight having "For Cast Crank 340 Only", or something similar.

If cast, the crank itself would have a thin parting line while forged has a 1/4"+ wide line.

Cart crank is on the left. The other may be forged, but has obviously been smoothed out/polished overall.

Chances are that yours is forged because forged cranks were used into '72.