The only complete, original, Steinway DR's (I've been told) are Mel
Septon's in Chicago, and the one in the Watkins Mansion in Winona,
Minnesota (part of an Aeolian residence organ.)  The mechanisms differ,
slightly, from those in smaller Duo-Arts, but I doubt that either owner
would be inclined to let anyone take them apart for engineering
drawings, should they find a gutted one to retrofit.

Still, the differences could be accommodated by a few modifications,
such as the making of a lever system that takes the 1" throw of the
striker pneumatics, then transfers it to the undersides of the keys via
poppets actuated by contact with the center of the levers (doubling the
force); and the installation of 2 pumps: 1 for the stack, the other for
everything else.  (That's all I know.)

Gordon Stelter
Athens, Georgia