If you want the factory setup, try to find a '64-6 A-body parts car with variable speed wipers. For ease of wiring and interchange, try to find a genuine '64 model. You'll need the switch and related wiring along with the variable speed wiper motor. The '65-6 use the same motor, but, the switch and wiring are a bit different, but, can be adapted. AFAIK the wiper transmissions are the same between single speed and variable speed those years, but, the '64 transmission pivots use bolt-on wiper arms, whereas the '65-6 use the push-on arms. You'll also need the wiring, washer pump, hoses, T-fitting, nozzles, and reservoir too of course. Early A's used the Jiffy Jet bag and bracket. Later models used the plastic reservoir. All '66 and earlier A-bodies used the remote pump that mounted on the inner fender.