I think it would be best to first contact the author, even if we are
not strictly required to. Maybe he will say "I'm still editing these
pages, could you wait two months before you put it in Wikipedia", and
it would be very impolite to deny that request.
Generally, when adding GFDL material, we have always added a
line at the bottom saying "An earlier version of this article was
based on bla bla by bla bla" and a link back to the original material.
See for instance [[TeX]] (which has improved quite a bit since we
imported it).
Axel