Vintage air in a 69 Dart

I am seriously considering this upgrade. I have a 69 GTS 340 with factory air. I am tired of pouring $$$$$ in to keeping it going. How hard is this swap??? Do I need a new air handler/heater box or will the new stuff work with the old box? Any fabrication involved? I don't mind doing some just curious how much if any.
I appreciate the input!