It’s not. My parents had a ‘64 Dart back when I was a kid that my older sister smacked a tree with and wrecked the grill. My Dad tried to fit a ‘63 grill from the salvage yard into it and it didn’t fit. Ended up bending and beating it with a mallet to make it fit. It never looked right, but at least it was better than the smashed grill it replaced.
As I recall, the biggest issue was the height difference. The ‘63 is taller.
