Harmonic balancer 340

73 was the only year for a cast iron crank in the 340.

Um no they also came in 1972.

Question for the original poster, are you using the new 1970 and up style timing chain cover that has the timing marks on the drivers side, if so I can measure from the back of the cover to the edge of the balancer to give you an idea if it is seated all the way on.