The mysteries behind engine balancing?

If you notice the 318-3 steel truck crank, that was recommended by Direct Connection, it didn't have a 5/8 hole drilled in the front & rear rod journals.

From what I was told, these holes were added to offset the weight of the 340 connecting rod on the steel 340 crankshaft.

With the exception of the 360, the 273,318 & 340 are the same size.
I could see using the 318 crank in place of the 273 & visa versa.
The balance would be close.

Ed Hamburger used to sell a blueprinted 318-3 crank kit years ago.
I used one in a 340 that I had balanced, with no concerns.
Their selling point was , it was stronger due to not having the lightning hole drilled thru the rod journal .