Thank you to the MMD members who responded to my request for
information, "Guide Pins Align Pneumatics to Action Stack", published
in MMD on November 29, 2012.

Stephen Toyne, of Boston, Lincolnshire, England, suggested that the
guide pins were probably installed by a previous rebuilder, rather than
by the original manufacturer, The Aeolian Co.  All the evidence gathered
so far indicates this to be the case.

I had previously learned that the 1935 Model L piano (Steinway 279076)
pneumatic system was partially rebuilt (Duo-Art B drawer, pneumatic
stack, and 15" Duo-Art pump) in Manhattan Beach, California, back in
November of 1975.

The use of guide pins before stack disassembly to align the striker
pneumatics on the decks later was confirmed by Tom Ahearn, of Topsham,
Maine, who knew of their application by Carty Piano Company in
California at that time.  A business card meticulously affixed to the
inner rim of this piano clearly identified the previous rebuilder as
Carty Piano Company.

The installation of the guide pins (two pins per striker) by Carty
Piano Company reflected extra work, but my effort as the second
rebuilder will be easier.  There are 40 strikers (7/8" wide) for each
of only two decks.  Therefore, lateral alignment of the pneumatics with
the backs of the piano keys is a bit more demanding than for stacks
with three decks and wider pneumatics.

MMDers may wish to incorporate similar guide pins in their pneumatic
stack rebuilding efforts for 'original' instruments, thereby taking the
'next' rebuilder into account.

Thanks again,
Bill Koenigsberg
Concord, Massachusetts