Honestly I've never seen one of the clutch arms with the offset hole in question.
I've only seen the "replacement style" with the hole in the center - I've also never needed to replace this part - only the bell housing or the pivot.
Maybe a member here with access to Ford documentation can look up this part and determine when and if it changed - there should be some revision history out there for the clutch arm.
I've had at least a dozen 6 bolt bell housing assemblies over the years and ALL had the center spring hole style end. I have one restored now with an original pivot in place with a '65 date code that will go back on my '65 K - and it has the center hole style arm - everything looks original, so I don't beleive the arm has been replaced.
FYI - there is a 5 bolt bell housing, clutch, & flywheel on eBay right now - and it has the offset stykle arm discussed in this thread.
Could this be a running change or part of the 5 bolt to 6 bolt design changes???? Could this have happened in the late '64 to early '65 time frame???