You will also find that the K6 right footpeg bracket is slightly longer than the K2. Why, i don't know 
Very interesting info and good to know.
I'll check the footpeg which is not original Honda, it's a Yamiya version on that photo with straight pedal.
I seem to remember one of the "F" models was fairly straight as they pivoted in the alloy footrest plate
Did the F model have the spring bracket for brake switch?
I saw that some later did not have it.
OK, not even Hondaman recognized it

I had thoughts about eventual early version and pipe had an indent for it...
Maybe a CB500 something...?