Carl,  If the kind of vacuum pump you are speaking of is a suction
box type that is normally used to electrify player pianos, I would
strongly advise against it.  The main problem is that the exhaust from
the impeller, which would be your pressure port, is passed through
the motor armature.  This is intended as a cooling measure.  The air
pressure that is produced has a good deal of heat which can be damaging
to pipes and chests.

I have a RAM orchestrion conversion that I am reconditioning for
a client.  It has an accordion that was running off the exhaust end of
the suction box.  The heat from that hot air melted the wax which holds
the accordion reeds on -- a veritable mess.

The blower unit that PPCo has available does not pass the air pressure
though the motor, which eliminates this problem, and it can be run on
a rheostat.

Brian Thornton - Short Mountain Music Works
Woodbury, Tennessee, USA
http://www.shortmountainmusic.com/