Johnson's size of ears, upturned nose at end showing nostrils, downturned brow ridge, deep set eyes, size of lips among other things make me think the man in the PC is NOT Johnson. The only similarity in features that I see are the color of skin and the mustache.
I also don't see how you can say that's Harry Buckner. The references for Buckner are so scarce that while it might be, I'd be far from comfortable with the ID.
My only point with all of this is that we shouldn't ascribe ID's which drive up prices if there is no certainty. That postcard was a $1200-$2000 postcard that sold for $6000. I think that's out of whack and though I hold Hakes in a very high regard, don't think it is right.