One suggestion for importing old archives: let LISTSERV do the work for you!

In other words, create a dummy list with a huge daily-threshold and all the
acknowledgement stuff turned off.  Then write a script to burst your foreign
archives into individual emails and send each one on to your dummy list.

LISTSERV happily processes them and creats a new notebook formatted to its
liking.  The original dates on the posts are not altered.  If the dummy list
has a different name then you can globally change it after the new archives
are created.

I have done this successfully with literaly thousands of posts from old
non-LISTSERV archives.  The exact method of getting your burst posts to
LISTSERV without adding any new To:/From: etc. headers is probably the
tricky part.  I did this on VM where it is trivial but I can't imagine
it's much more difficult with any other system.  And compatibility of the
new archives is guaranteed :-)

--
Bill Gruber
City University of New York