Harmonic Balancer...

[all_about_cars]

You should see where the timing tab is. I believe the earlier balancers have. The Top dead center timing mark on the balancer in a different place. Earlier engines had timing tab toward right side looking at the front of engine and the later engines were located at the top of timing cover. If removing balancer to get cast number is an option I would do that or at least do some research. Hope that makes sense on the timing tab reference.