I have worked with brass trumpets, including North Tonawanda.  The
overall nominal tuning of the organ -- the violins and open flutes, in
particular -- is the baseline for where the trumpets need to be tuned.

A set of brass has some half-length resonators, and it is imperative
to get correct resonators assigned to their proper note and octave.
There may be two "G's", an octave apart, and they both use short
resonators, but the resonators will not be the exact same length.

With this task done you must find the tuning where the trumpets sound
best -- best timbre (close to "nominal" tuning mentioned earlier) --
and then adjust the organ a bit sharp or flat to accommodate this.

In any event, the trumpets will not all sound equally fine (and
some may not sound even acceptable) without some finer adjustment
to resonator lengths.  This step is very tricky, fine work, and should
be done by an expert.  The great news is that no organ sounds as
exciting as a brass trumpet organ with properly functioning brass!

I have a fair number of resonators of all lengths.  My web site will
be getting a huge update right after tax time.

Alan Erb
http://www.mechanicalmusicbox.com/ 

 [ See the photo of a set of beautiful North Tonawanda trumpets
 [ at http://www.mechanicalmusicbox.com/images/dntonawanda.jpg 
 [ -- Robbie