Yes and no about it being the same. Both are cast cranks, but the 318 cranks are internally balanced. The 340 cast cranks are heavier duty cranks and are externally balanced.
@luvmopars If the crank isn't rusted up and is still standard, AND you still have the harmonic balancer unique to those cranks.....$50 to $100 maybe. The main ones that would be interested would be someone doing a restoration and needing a good original crank for a late 72 or a 73 340.