There are several ways to gain more clearance in certain players, and
regular uprights, to allow the installation of another make of player
action.  These methods apply to both player and non-player uprights.

Consider yourself warned: this takes skill, and should never be
attempted unless you have the experience.

This "trick" is very handy and required when faced with installing a
tall stack into a piano when the sticker-to-key clearance is a little
bit short.  The finished modification is invisible if done right.

Most pianos with a one piece top have a 5/8" strip of wood glued across
the top of the strung back (plate).  In this case you can usually gain
from 1/2" to 5/8" extra clearance (depending on the actual thickness of
the board) from the tops of the keys to the whippens without modifying
the cabinet at all.  You can use this wasted room for vertical
clearance for a tall player action with some work.  While 5/8" doesn't
sound like much, it can make a vast difference whether many player
actions will fit or not.

You can remove this wood strip and reglue the sides on the piano to be
flush with the top of the strung back, making the strung back higher in
the case than it was originally.

Locate the hammer striking point, and mark it.  It is a good idea to do
this before restringing, because you can see the hammer and damper line
on the old strings.  Don't remove or monkey with the upper plate-to-
action posts at all.

Three major things will have to be carefully done in order for this to
work:

First, a strip of wood must be installed on the bottom of the strung
back the exact thickness of the wood that was removed from the top, and
drilled to reinstall the rear casters

Second, the keybed must be notched to allow the keybed supports on
the plate to go up into the keybed the equal amount that the strung
back was raised.  *Do not cut these supports off or modify them in
any way!*

Third, the action stickers will no longer reach the capstans.  Keep
this in mind.  The piano action must be in the exact position to the
strings and strung back as it was originally.  The keys must engage
it where is belongs, and do not lower the piano action for any reason!
To do so will ruin the tone of the piano!

Okay, the action cannot be lowered, and the keys cannot be raised.
Even if that would work (which it won't) it will only loose the
vertical room that had just been added.

Measure the distance of the four keybed action brackets, and jot down
the measurements.  Remove the action brackets.  Glue four 2'x2" pieces
of wood, in their location on the keybed.  Use the exact thickness of
wood as the board you removed from the top of the strung back, and
reinstall the action posts.  The action should now fit properly, if you
were very careful with the measurements.

The stickers will now be too short.  The best way to fix this is to
install a new longer set, or it is also possible that a longer set of
stickers from a junk piano action will work.  Extra long capstan
screws would work in this situation, but I don't think any are made
like that.

If new or longer stickers are not available, remove the keys and
capstans and glue small wooden blocks on the capstan end of the
keys.  Redrill and reinstall the capstans.  Very light wood should be
used so the touch of the piano will not be affected, such as basswood,
or a good quality balsa.  Junk piano keys are the ideal material to
make some riser blocks from.  Be sure not to glue the blocks on the
key-ends in such a way as to interfere with the bottom tier of the
player action.

Regulate the capstans, and make longer pedal dowels.  The piano will
not play or look any different than it did, but it will have more
vertical room for the player action.

Horizontal Clearance.  (Mostly needed in non-players)

The best way to "playerize" a regular upright is to knock the case off,
and modify a player case to fit the strung back, and have a new set of
keys custom made.  In some players and non-players made by the same
company the strung back is the same scale.

The above described method to gain vertical clearance will work on
regular uprights too, but usually the sides of these pianos are not
nearly as wide as a player, and that is where you are going to run into
many problems.

Many old non-players have about 1" extra of keys that run behind the
capstan.  The following changes the touch of the piano somewhat, but
the front keyslip can be planed down, and the key-frame, fallboard and
cheekblocks can be moved toward the front by the same amount, and the
capstans relocated further back on the keys.

This, coupled with disabling the folding fallboard, will usually
allow the installation of a small player action, like a single-valve
Standard, two-tier Cable, Aeolian or Baldwin.

The best way to install a spoolbox in a non-player upright is above
the hammer line.  like Cable Euphonias and early Kimballs.  This is far
less intrusive than having to modify the front panel.

Good Luck!
Andrew Taylor