Thank you, Eli.  More on the Duo-Art system as installed on my
Mason & Risch.  It was certainly factory installed as the case of the
piano is exactly as it should be for a Duo-Art system.  Yes, it is an
above-the-keyboard installation.

The odd thing is the assortment of parts from different Duo-Art eras.
Even the tubing design and circuitry is somewhat different than
anything I've seen in the literature, but it all works as intended
(as near as I can tell).  Incidentally, Terry Smythe, who lives just
a few miles from me, had the twin to this piano at one time in his
collection.

With regard the operating vacuum on my piano, I am quite pleased with
its dynamic range with the maximum vacuum set at 45 inches.  However,
I am interested in what it was "designed" to be as this value would
(in theory at least) provide the most accurate playback of an artist's
performance.  I may not adjust the vacuum back up into the stratosphere
even if it was designed to be there because I would suspect the 70+
year old piano action will survive much better not being pounded quite
that vigorously.

Alan Turner