Oh, and I forgot "The History of the Emanuel Moór Double Keyboard Piano", Herbert A. Shead, 1978, printed and distributed by Unwin Brothers Limited. ISBN 0 9506023 0 2 As far as I know, the only book on the Moór double-keyboard piano. Well-researched, with line drawings/diagrammes, and a fold-out wide page with drawing of Beachstein Moór action.
This PTG archive page provided courtesy of Moy Piano Service, LLC