**1973 bastard 340 balance??**

I have done some research and found out that the 340 I have is a 1973. I know that 72-73 had Cast Cranks in the 340's and they were supposed to be externally balanced but different than the 360 is balanced..... So if it is supposed to be externally balanced but balanced different than ALL 360's...... How were they balanced different??

Can someone shed some light on the subject?