Front axle, springs with hangers, and brakes from a 1971 or earlier D100 is probably your best bet. I would grab all the steering components including the column, too. It also already has a 4-1/2 on 5 lug pattern to boot. You could probably convert to front discs if you wanted, but the drums would be okay in my book. The 1966 Dart has a track width of 591/2 inches, and the D100 has track width of 60 inches. Nothing a little wheel backspacing adjustment wouldn't fix.
