1972 Timing Pointer

My pointer is much simpler and it's attached by two bolts. Which style was used for which years? And where can I get that earlier pointer? Does anyone have a better photo of the pointer? And what is the purpose of that "extra" arm with the knob on it?
Here's my pointer.

Dave,

Your timing pointer is correct, as it appears to be identical to the original timing pointer on my '71. The timing pointer in the pic of Mike's is for a later motor, or it might be a superseded replacement part. I think that the "knob" is for an inductive pick-up.

John

I though Mike's was a "one of" too, but here is that same pointer on another car. That knob does look like a crank position sensor, but I think the 351-C was retired long before that technology was offered. And judging by the "patina" of this pointer, it looks like it might have come with the motor.

Dave,

I agree that the sensor tech came well after the US production of the 351C ended. The pointer could be from a 351M or 400, or just a replacement.

Here is a pic of my original '71 pointer.

The open loop thingy on the end of the timing mark was for a sensor used by Ford dealers. It dropped into the hole so they could check ignition timing without a separate light. Later, the factory discontinued degree marks on balancers altogether and only used this device; the original pre-computerized-engine smog laws were designed to make changing ignition timing more difficult for owners. Thank your elected members of Congress for all such mechanical nonsense.