Most very early player pianos were no deeper than a plain upright,
or else they had case extensions glued and doweled on the sides and
were equipped with a longer keys and key bed.  Another tell-tale sign
of an early player is that the wippens are not of the player type,
but have a hole drilled through them with a jack let-off button
installed.  (I've done this with retrofits; it's tricky).

During the years, I have successfully  retrofitted several plain
uprights with pneumatic stacks, simply to build something useful out
of spare parts.  This has been challenging, but I've learned a lot
about upright construction, and what the old makers did to make room
for the action stack.

I have always avoided installing the stack under the key bed, unless
it was a small console piano.  This makes both the player and piano
most difficult to service, and although I am sure to get some
disagreement here, I do not think the performance is nearly as good.
Also, in such an installation the key bed plate supports are often in
the way and must be sawn off.  I do not like doing this, but if I have
to, I will install a steel "L" channel under the key-bed, fastened to
the sides.

There are many cases that a ordinary upright has too little vertical
clearance for a pneumatic stack.  There are several ways to correct
this that will be invisible in the finished product.  Pianos with an
'Empire' top often have a 5/8" strip of wood running along the top of
the pin block.  If this is the case, remove the strip, remove the sides
from the strung-back, and re-glue the sides even with the top of the
plate, making the strung back sit higher in the case, notching the key
bed slots for the plate supports an even amount.  Install a similar
piece of wood on the bottom of the strung back, notch and re-drill for
the casters.

If the plate has no wood strip above the pin-block (such as most
two-piece tops), simply lower the key-bed within the case.  Usually the
amount of lowering needed is quite small and will not make the piano
feel unnatural when played.  By repositioning the front panels carefully
on the front and trimming the pilasters, this is not noticeable when
the instrument is put back together,

In either case the action will no longer meet the keys or the lower
action brackets, but this easily correctable.  Install riser blocks on
the keys (note that most player pianos have this) or install the longer
grand capstans on the keys.  Regarding the lower action posts, obtain
some 3/8" all threaded rod, top them with acorn nuts, and reinstall.
The action will sit solidly on the acorn nuts without rocking.

The important thing to remember is the action _must_ sit in the same
relation to the strung back as it did originally, maintaining the
original hammer striking point.

The stack must have enough clearance to fit under the wippens plus
enough vertical height to prevent the rear of the keys from bumping
into the stack when the piano is played by hand.  Usually the rear of
the key-cheeks must also be planed down to accommodate the stack.

Regarding depth within the case, this is a little more tricky.  In most
cases, the folding fall board must be disabled, but if it is carefully
removed, the remaining piece can be made into a care extensions for the
front panel.  If this is done carefully enough, it will look like it
belongs there.  The front panel can also be planed down on the back
side for clearance for the roll motor.  I have also pulled the key bed
forward, and relocated the capstans on the very back of the keys, but
this also changes the touch of the piano, and is not recommended.

This is more work than most rebuilders are willing to undertake, but
the fact is that there are many great old uprights around and they are
inexpensive.  As with anything custom built, my work will be examined
under a microscope by my rebuilding peers, so with this type of
project I do the best as humanly possible, using parts that would
probably be scrapped by now.  I enjoy the challenge, and the resulting
instrument that emerges is just as enjoyable as any other pedal-pumper.

Andy Taylor