There's a difference between being a naysayer (it can't be so) and being a skeptic (show me).

The OP states he has a '68 crank which would be forged. The typical forged crank flange is shown in the diagram below. Both the initial drilling and the final bore are sufficient in diameter and depth to clear the .750" pilot on a 833.

Yes, some later cranks have only a "divot" instead of a drilled hole but I've never seen (not the same as saying it can't be) a '68 like that, that's why I asked for a pic...for my own edification.