What IS this?

When I bought a dis-assembled 1966 Barracuda a few months ago, the seller included a LOT of extra parts that I've been sorting out ever since. Except for the piece shown here, I've been able to identify everything. I KNOW it's not for an early Barracuda because it's too long, but the width is just right & where the gas filler cut & spare tire well line up fit the Barracuda perfectly - so I'm thinking this is for an early ('64-'66) Valiant/Dart? Can anyone tell me exactly what it fits? Valiant? Dart? 2 door? 4 door? It looks like new. I'd like to sell it, but I don't know what I'd be selling. I've looked all over & can't find one of these anywhere. Maybe I'm looking in the wrong places. :)
I hope you can make out the pictures....
Thanks, Mark

Floor Pan II Valiant (maybe).jpg

Floor Pan Valiant (maybe).jpg