I just cross checked multiple shock listings and it looks like the Valiant uses different shocks from the Dart or Barracuda in '66. I don't think they will fit on your car. :(
Got to fit for sure Ddaddy, Barracuda and Valiant shre the same belly .. I have seen this before and it is just because the valiant was over looked in so many parts places .. same as a Barracuda sir