John,  pipes tend to not be too much out of tune (unless you took
them apart to repair them).  I would "sample" a few pipes with a pitch
measuring device (an electronic tuner or tuner app on an iPhone) to
determine what pitch was originally used.

We aren't talking whole steps, but just lower (usually lower)
frequencies.  For instance, in the piano world around the 1900, and
even later, pianos were designed to be tuned at A=435 Hz, known as
"International Pitch"   This was sometimes even cast into the
plate.  The modern standard is A=440, but some Russian pianists prefer
A=445!

The reason to try to find the original tuning basis is that most pipes
don't have enough tuning adjustments to be tuned to a higher or lower
standard, reed pipes especially (and reed organs too!).  Air pressure,
too, has an effect on pitch and voicing.

David Dewey
Oroville, California