Dear Mark, the wildest part of the issue is that the ratio of an ASC is more or less the one of an AM - so the sense of the freewheel converter on an ASC escapes me completely, excepting use on bikes with very low b/b heights. Perhaps.
What I really think is that the converter is for use on a TF / T hub -
this was the pre-WWII stepped shell two speed that had an external freewheel. In my box I´ve got exactly the item shown in the auction you mention, and it was on a T which I "converted" to a TF by substituting
the freewheel by a simple sprocket. I do hope I remember this correctly.
Regards, Toni Theilmeier.