How interchangeable are 318 harmonic balancers?

Professor Fate said
The timing mark changed location in '70 when they changed from the cast iron water pump with a drivr's side inlet to the aluminum pump with a pass. side inlet.
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That seems to agree with what I have here (fuzzy freeze-frame screenshot from a video I sent the owner a few days ago):

Screenshot (52).png

I'll check the bolt spacing tomorrow evening after work, thanks.