> I also have wondered what sort of heads were used for wire recorders .
> (Weren't flight recorders a wire recording until reasonably recently?)

As I recall, flight recorders used steel bands (and still may).

If one is looking to play back some pre-recorded wire, my
first suggestion is to pick up a wire recorder transport.  They
show up on the ebay auction from time to time.  I used to
own one, and it really didn't sound as bad as I expected.
The head had a very deep notch in the front to capture the
wire, but I never tried to take the thing apart to see how it
was built.

The transports (most were made by Webcor, a few by Brush)
did not use a capstan; instead, the takeup reel turned at a
more-or-less constant speed.  This means that the wire itself
passed over (through?) the head faster as more wire
accumulated on the takeup reel.
The head had a really cute mechanism to move it up and down
while running, to make sure the wire wound onto the takeup
in a nice even pattern.

It shouldn't be too hard to infer the playback EQ by inspecting
the rather simple electronics in the machine.  You might put out
a feeler on the rec.audio.tech newsgroup.  Some people there
do serious archiving work, and can probably elaborate at length.
For now, back to the pic world.