Hello MMD.  John Tuttle's query will surely produce a large number of
replies, but, just in case: the U.K Player Piano Group sells a diagram
of the layout of a Half Duo-Art.  The layout isn't exactly the same as
that of my Steck Half Duo-Art, but it's not very different.  I'll bet
that Julian Dyer responds to John's query, but here is the web address,
anyway:  http://www.playerpianogroup.org.uk/

Good luck,
John Phillips in Hobart, Tasmania