Agree that you can do it as long as you swap over the Dart front fenders, hood, front bumper and front valence panel. The Canadian 63-64 Valiant Signets were actually the reverse of what your plans are. They had the Valiant front end on the Dart body.
http://autosofinterest.com/wp-content/uploads/2015/05/1964-Valiant-med.jpg
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