340 cast crank balancer

Is it different from a 340 forged crank balancer or a 318 cast crank balancer? (I thought they were all the same until the externally balanced 360)I know I have a 318 cast that I have to pull in the coming weeks, and might have a 340 forged kicking around....

The balancer he needs will say "340 Cast crank only" on the front of it. They came on LATE 72 year model 340's, and all 73 year model 340's.