Correct me if I’m wrong, but I believe that a despecialized ROTJ would be pretty easy to throw together. Ghost Hayden and Naboo in the celebration montage are the only differences between the 97 and 04 versions that I can come up with.
I believe there are also differences in the Coruscant background during that montage. But yes, I think the main work for putting together the 1997 version would be rotoscoping that shot.