> unix machine, if that matters.
 
Yes, it matters greatly.  Not only that, it matters what mail user agent
you use.  I happen to use the EMACS rmail suite, and it's a simple
matter to cook up a macro to convert any given format of digest into the
one expected by the undigestify-rmail-message command.  I once did it
for the format of LISTSERV log files.  It should even be possible to
augment rmail so it recognizes LISTSERV digests, but that opens another
can of worms.  In any case, if the digest is already in your RMAIL
file, it should need little more than a replace-regexp to convert the
separators into lines of hyphens and a change of the outer "To" and
"Subject" lines to "Info-blah" and "Info-blah Digest ...".
                                  John Chandler