72 340 balancer

Early '72s were forged crank and used the internal balance balancer.
1686971102848.png
Late '72s went to an externally balanced cast crank (and lower compression and smaller 1.88 vs 2.02 valves) and used the "cast crank 340 only" balancer.
1686970914172.png

1686970941995.png
The changeover came sometime during mid-year, so it depends on what crank you have.