I'd probably suggest Castle 2, it's a fun one to play on and the architecture matches better than Castle 4.
That being said, it wouldn't take me long to convert small village to a siege map, so that's also an option. Just close the doors, move the ladders around a little, throw up some temporary barricades and move the spawn positions.
Problem would be GoN getting the map file, but I'd be happy to throw up a temporary dedicated server for the match. They've added automatic map downloading in the .120 patch, so if that's officially released before the match it'll make things a lot simpler too.