I'm trying to conjure an accurate memory of the "preggers" Roto-Swirl on our 1960 Kenmore. You are right about the bottom ends of the vanes; it looks distinctly like a RS there. However, this agitator differs from an RS in that the vanes didn't start right at the top, as they do on the Mitrade.
Interesting! Have not seen an agitator quite like this one, before.