A comment on some boards (can't remember where) got me thinking. Take the abandoned Maztica 2e setting. In the Forgotten Realms 4e history, this continent (basically the entire western hemisphere) of Toril is shunted to somewhere else. Spellslinger is a fantasy based wild west type setting. Take the shifted Maztica setting & place the Spellslinger setting north of the original setting. Then forward the timeline about 300 years.