The rma department sent me back a 580 in a 570 casing.
Haha seriously! That's insane. I see your predicament though... stuck with a 580 & 570. As unfortunate as it seems, you probably would be best off getting them to change the 580 for a 570. OR (pretty unlikely) if you paid them the difference, would they change your 570 for another 580??? and SLI 580. Again want to be sure your PSU can handle it.