I wouldn't be surprised if the early Lancer/Valiant used the same or similar pan as the '63-'66 As. It would've been easier in manufacturing I would think.
So vntned, I guess I don't need to worry about hijacking your thread since you were the OP!
I can tell you that the '63-'66 Valiant/Dart pan is about 3" wider than the '60-'62 Valiant/Lancer pan but seemed identical otherwise. I installed a '63-'66 pan on my '62 (couldn't find one specifically for the '62) by cutting off about 1-1/2" on each side. But the difference in pan width didn't seem to cause any problems when I installed the USCT Level 1 kit.