340 Identification.

That balancer is not a 340 cast crank balancer. The correct one is pictured in post #4. It says right on the front "340 cast crank only". This is the only balancer ever used on the cast crank 340.
So its either a forged crank or someone put the wrong balancer on it. Pull the pan to find out, its the only way. Some of the early 72 340's had forged crank still, maybe you got lucky.