I finally looked at the tubing in a Nelson-Wiggins 6.  It is an original
machine with what I believe to have the original tubing in place.  There
are two pneumatics that switch the wood block on and off and one that
switches between snare and tambourine/castanets.  When the xylophone
comes one the wood block is turned off.  When the soft pedal is on the
tambourine/castanets play instead of the snare drum.

Hope this helps.
Don Teach - Shreveport Music Co.
Shreveport, Louisiana