You could ofcourse bother to copy them from map to map in level editor. I did this for N-pulse a while ago (not a huge overworld) anyhow this will hardly cost you a few hours. Ducati also did it (with a way bigger OW) anyhow just try it...
And as for GMAP questions.... there are tons of FAQ/Walktroughs and how-to posts/threads on these forums & in the Graal Bible
You might even want to try and use Rick's GMAP naming system...