Balance Issue / Vibration

BTW my 68 340 block was fitted with a cast crank by a previous owner.
I'm thinking mine is a forged crank in a later cast-crank block, based on the paint scheme clue. The VD appears to have only three dimples or shallow holes machined into the face.

Would those round dimples maybe correspond to the slot or weights for a cast crank/externally balanced engine?