I just bought the Vintage Air kit for my '72 Cuda and am in the process of installing it. Everything is included in the kit, all the way down to the extra crank pulley and belt. The only thing it looks like I'll need to buy is new heater hose and R134a freon.
To answer your question, the Vintage Air kit includes a large round plate that covers the hole in the firewall. This plate has four holes in it in which the two heater hoses and two freon lines enter.