I think the reason people want the 822 crank is that that's what Colvin's book says you need to have. So everyone building a 67Z wants the 822 crank with the telltale notch. This isn't something that even the diamond judges are looking at so Colvin's book is what we're using as a guide.
When I rebuilt the engine in my 67 Z, I replaced the 6467 crank with an 822 because that's what I believed was correct. Picture below isn't great but the 822 has a single pie-shaped cutout on the rear flange:
Now, after some years have passed, I'm also starting to think Colvin was wrong and that the 6467 is the correct crank. Convincing arguments are from the chaps who've taken apart original engines (Zedder and 427King earlier in this thread), plus the fact that my engine still was standard bore and had the factory unique dome-shaped pistons and connecting rods in it. Why would somebody swap the crank only?
What did I do with that old 6467 crank you ask? I think I sold it to "budnate" at the last swap meet I was at and sharing a booth with him.