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