The pneumatic stack described by John Grant seems likely to have come from a Duo-Art; the note count and location of the division point
supports this premise.

After the merger, several Duo-Art variants were produced that utilized modified Ampico B drawers.  Some, but not all of them were equipped with pneumatic stacks nearly identical to the Ampico B.  Others, such as the example owned by Bill Koenigsberg, employed another type of stack quite different from Ampico.

The next question that comes to mind is the expression regulators.  Were they attached to the underside of the stack as with a customary Ampico B?  A photo would be very welcome here.  If conventional Ampico B curtain valves should be present, the Duo-Art theory is likely not correct.  Photo, please!

Dave Saul