Hi Kim,
It appears to me that what you are working from may be
over-edited, not uncommon in editions from the 1950's and before.
Not all editors of modern editions have made the choices
that later editors might have chosen. For example shifts
of 2 x 3/8 to 3 x 3/8 simply mean the editor's choice of
where to put measure marks causes measures of different
length. It's usually preferable to let measures have
different lengths; changing the time signature makes
more for busyness than for clarity.
Changing measure lengths is often done to avoid
having notes that span measures. Another approach is
to use mensurstrichen (measure marks between staves rather
than through staves) and let note values slop over the
measures. That better expresses the way the music was understood
before measure markings came in with the Baroque,
which has far more regular rhythms.
Also, shifts between 6/8 and 3/4 in some repertoires can
be ambiguous and fluid, often off the beat. Explicit call outs
reflects the editor's choice of phrasing, which properly should be
determined by the performer.
If you can, look at a facsimile of the piece you are transcribing,
use the modern edition to help you where necessary, but
don't slavishly follow it. Avoid being specific where the original was not.
In any case, while trying to get LilyPond to produce the time
markings you desire may be technically interesting, from a
practical musician's standpoint, those markings are unnecessary
and distracting.
Bockett Hunter