Hi Tim,  I did one of these instruments a lot of years ago and am
pretty sure I made a sketch of the tubing configuration at the time.
Finding it now will be a challenge as I have moved about four times
since that restoration and lots of stuff has yet to be unpacked even
for the first time.  I'll have a look and maybe we will get lucky!

Coincidentally, I have just ordered high-resolution scans of the two
"C" size drawings (one for grands, one for uprights) that were bound
into the back of an original Welte (Licensee) Service Manual I own.
I plan to have initial (unedited) prints of these at the 2012 AMICA
Convention for "show-and-tell" and will be taking orders (price not
yet established) for cleaned-up copies on nice vellum or other sturdy
engineering papers.  Unfortunately, these drawings antedate the design
with the multi-chambered change-over unit, but I'll keep looking for
my sketch.  Also, check the MMD Archives; there's a small chance
I submitted the sketch there or possibly in an AMICA Technicalities
collection.

John Grant