Internal/external balancing

I have a cast crank 340 listed now. Someone said the change was like February of ‘72 was the change to cast crank, low compression pistons, and the balancer and weighted converter.

the timing cover change was after 68 from what I’ve seen. Went from drivers side to passengers side, and coincided with the release of the 318 and 340.
Cast crank was late ‘72 model year change. I also have a ‘72 forged crank engine...