I believe the book Bruce Buchanan is looking for is the late
Charles Davis Smith's three-volume Welte rollography-history.
It was edited after Charles' death by Richard J. Howe and published
by AMICA. I believe all copies were sold, though it should be
available on inter-library loan.
However, since the work focuses on the Welte reproducing piano,
not on organs, and contains virtually no technical data, though much
historical information, I'm not sure it will meet the needs expressed.
Mr. Durward Center, a virtuoso restorer in Baltimore, Md., is a man
I'd turn to for Welte technical help. His email address is
Durward Center <firstname.lastname@example.org>