Love sequentials. First car I recall seeing with them was a Cougar.
Not feasible for a 69 Dart but maybe concentric sequentials from center to outside would be. Trouble is that level of electronics is over my head.
Oddly enough the "Digi-Tail" 1969 Dart lights are sequential apparently. $ 189.00. When I spoke to them at the time I was building the Dart they hadn't released them yet, but they have since. I built my own.