Eli Shahar asks, "On the spring pneumatic, there's a very small
pneumatic which counteracts it; what does that get connected to?"
I am happy to answer this question, and add a few tips.

There are two small compensating pneumatics attached to the top of each
spring pneumatic, one for bass and one for treble.  These both connect
to a tee at the top of one of the two unit valves that operate the
sustaining pedal pneumatic.  When the sustaining pedal is on, vacuum 
is also directed to these two small pneumatics.  The purpose of these
pneumatics is to compensate for the reduced suction intensity required 
to strike a note, when the sustain pedal is on.

Be very careful to insure these two small pneumatics do not leak the
least bit.  Their supply is minimal.  Any leaks will render them
useless.  After I carefully recovered mine, I connected a test hose to
them and submerged the entire pneumatic in a glass of water and blew
into the hose.  Even though I was very careful, I did find a leak,
which was obvious when bubbles came from the hinge end of the pneumatic.

Bruce Clark