On several occasions I have faced the very same dilemma when adding a
suction unit to a customer's piano.  A couple of other suggestions come
to mind.  First if you are restoring the player system you can always
trim one of the reservoirs before covering it say 3/4 to 1" in width to
allow for more access.

If on the other hand the reservoirs are already covered you can make
some additional room by replacing the factory sides of the suction box
with material slightly thinner.  Most suction boxes come with 3/4'
particle board used.  If you substitute 1/2" on two of the opposite
sides you have in effect created an additional 1/2" of space.  The
noise difference is negligible.

One additional problem with installing suction boxes is the possibility
of having to re-route the pedal linkage, especially the soft pedal.
I once ended up placing the suction box on the toe block of the piano
which was right in the path of the soft pedal dowel.  The solution was
to install a couple of transfer levers like are used on grand pianos.
This allowed the dowel to be in one spot going up between the reservoir
and the suction box and then the motion to be moved over to the original
location as it passed through the keybed.  Practical engineering is
what makes this all fun.

Norman Cantrell