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As you say, the picture is not very sharp, but is similar in almost every detail to the 1926 York Eb at Horn-u-copia, so I don't think it is a case of the wrong bell being put on the wrong body.

I have never seen York "short action" valves either, although my c.1913 York althorn has hollow, built-up rotary valves to reduce the rotating mass, so they obviously knew what they were doing, even then!