If as Ash say's its the same fit as the 400/4, And if Ash says so....it is,
I think I have one in a box somewhere that you can have but you'd need to weld one a 'fasioned new'and longer foot.
Would that help at all?
Let me know and I'll go have a dig about in the 'graveyard' shed. It's off a 1977 cb400/4F