I have restored numerous Duo-Art stacks and it seems most of them
Are made of poplar, or something of darker color, close grained,
that I can't make out a wood type on.

Once I had a Steinway that was built in late 1929, a very expensive
Chinese painted art case piano which I am sure went out for painting
for most of a year.  I am judging that the stack went into it after
1930.

This is the only Duo-Art stack I ever saw made of pine.  During the
depression I am sure they cut corners to save money.  It needed extra
sealing of everything.  It worked beautifully, though, once finished.

I had one late Steck Duo-Art that had an upright player stack fitted
under the grand.  Everything else was standard Duo-Art and it played
just as well as if it had had a grand stack.  I just thought that was
wild.  It looked like they had must removed the spoolbox shelf and
installed it under the grand.

The Ampico stacks I have owned and rebuilt all seem to be of hardrock
maple with poplar pneumatics.  The valve blocks seem to be that same
darker wood that was in Duo Art.  Anyone know what wood that is in
Ampico valve blocks?

Of course the Ampico decks hold lots of weight and must withstand those
threads on the rods that hold the valve block on.  I would advise you
to make your Duo-Art stacks out of poplar which is very airtight and if
you use dried wood should not crack readily.

I did have a pipe organ chest my builder made from poplar and its
pouch board inside started having green wood problems.  Two years after
manufacturing I discovered it had cracked, opening up several notes at
a time to cypher.  Some dowels between channels, some glue and pneumatic
cloth, took care of it and the organ is still playing well after 15
years later.

D.L. Bullock
http://www.pianoworld.us/