I'm guessing Mayday Chimera's are going to work as well, like most recent FFG game with cards this size.
Well this video actually suggests the Mayday American size (purple sleeves) and not the Chimeras.
I know the Chimeras are used for other FFG games like Cosmic Encounter and Wiz-War, and, while the Americans are used in games with cards from Fluxx, Bohnanza, Bang! and Ghost Stories. Can anybody eyeball the cards when they get it and guess which one might work best?