Hello MMD.  My query in MMD 080518 elicited me several very helpful
direct replies.  I think I have responded to all of them; suffice to
say here that I am most appreciative.

In case anyone else is interested in this information, an article,
"Parting Is Such Sweet Triumph," by John R. Grant, on splitting open
the Duo-Art expression box, was originally published in the December
1979 AMICA Bulletin and re-published in Volume IV (1978 - 1980) of
AMICA Technicalities.

The article by Mike Kitner, Vestal Press Technical Series No. 5,
Rebuilding the Duo-Art Reproducing Piano Mechanism, is available from
John Tuttle's PlayerCare web site.

And finally, the reference that Robbie added to my original query,

  http://www.thepianoworld.com/technical_tips/duo_art_expression_box.htm

contains a wealth of excellent color photos and advice, thanks to Doug
Bullock.

John Phillips in Hobart, Tasmania