A lot has been written and speculated about differences in organ tuning.
Some facts:

 - Gavioli and predecessors (Marenghi, Gaudin, Frei, Mortier) used to
lay out their scales with low F or G as lowest bass note, and the
lowest note of the accompaniment and melody sections was G.  These
organs transposed a minor third up, so the effect was an organ playing
in B flat.

 - Limonaire and most German organ builders did not transpose their
scales, but they usually start with low C in the bass and melody
sections.  In effect they sound higher than the "high-pitched" French
organs!

 - Wilhelm Bruder Soehne and Ruth used a scale that transposes a minor
third DOWN-wards (C=A) for a deeper and more resonant sound; their
scales start in C, like the other German makes.

Cheers! and "vroulek Paahsen" from Holland,

Hans van Oost