Realizing that I forgot to mention the way I fix tracker systems that
don't have cutouts, I might add this suggestion.

Mike Kitner had a good idea, I thought.  A mechanical "lock", which
is probably a pneumatic with a finger extending backward from its hinge
to press against the tracker pneumatic, bringing it approximately to
the center position.

The problem with any tracking system on reroll is in trying to get
a roll back safely when the tracker had to track the roll at its
extremes.  Today, the best rolls are in the worst possible condition
because they're the ones played most often.  So your most valuable
rolls are the most vulnerable.  These problems weren't apparent when
some of the mechanisms were first designed.  So to add a helper
pneumatic or cutout and spring that improves the roll's chances of
survival is a very important suggestion.

The Standard Action Player and others have a flat spring that gradually
returns the bellows all the way up and sends the roll core all the way
to the left.  That would tend to cause the roll to pile up on the right
"fixed" roll flange, except that the weight of the cam arm is down, so
the overall effect it a very slow recentering movement.

The later Aeolians cut off the tracker finger ports to the dual tracker
bellows and left the vacuum on, so that if the bellows were equally
airtight, the system would center itself quickly and stay rigid.
However, this system for some reason tends to tear more rolls on rewind
than the Standard, possibly because it immediately centers, whereas the
Standard Action begins at the extreme it was brought to by the roll and
very slowly returns.  That makes more sense to me.

So for my tastes, a centering device like Mike Kitner recommends --
with a bleed in its supply connected to the motor governor line where
the vacuum is still regulated and won't be overwhelmed by a suction box
-- is a good idea (depending on how large you make your pneumatic, of
course).  And the vacuum line originally connected to the tracker
pneumatic should be stack (playing) vacuum instead of coming directly
from the pump.  These players usually don't have Themodists, anyway.

One other small suggestion as a touch would be that you try a flat
spring in place of a rigid centering finger so the tracker can be
centered gradually.

Craig Brougher