Power Steering Conversion for a 66 Dart 270

In general, look for parts/kits for pre-'70 A bodies with a 273/318/340.
Power steering also requires a shorter steering column, so a swap to a PS column (I believe up to '66, floor shift) will be required, or shortening of your current one. Many people go the opposite route, changing from power to manual, so you may be able to work out a trade on that...