If Americas, then Anchorome can work, with Greyhawk on south side of the large lake there?Dunno about Blackmoor but I reckon Greyhawk would fit pretty easily somewhere on the shores of the Sea of Fallen Stars.
Yeah, that would be reasonable enough: there is a Mesoamerican jungle across the ocean to the South of Greyhawk.To match up with world of greyhawk Oerth, maybe put both in Anchorome?
I seeI'd be tempted to put the Flannaes on the other end of the big old desert to the East of Faerûn.
That could work: my inclination would be to replace Kara Tur with the Flannaes, however.