installing AC in my 64 Dart

Some have installed a factory AC box. I know for 1965, so probably would fit 1964 too. I was tempted to buy a complete system a guy was selling for $100, but found you must cut new holes in the firewall. I decided I am OK with the under-dash unit that came with the car. One advantage is that I can change my heater core without venting my refrigerant as you must with the factory setup.