WTB Radiator - 64 Dart - 273
Based on Oklacarcollecto's post... I hit Champions website... They do have a '64 Dart 273 All Aluminum 19" Radiator! If you don't care about originality and want to drop in a shiny aluminum version they got it! And it's reasonably priced in my opinion.
http://www.championradiators.com/dodge-dart-radiator-1964
Personally, I'm still looking for the era appropriate version.
Great info though guys.. thanks much!