I'm nobody's idea of an expert, but maybe I can help a bit. I'm pretty sure the new wheel you are installing is for a later car. I don't know if that's a factor in your situation or not, but this is what a 69 Dart wheel looks like. Obviously I'm missing the horn parts, but the wheel itself is entirely different than your photo.
@str12-340 is pretty well versed in early 70's Darts, perhaps he will chime in.
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