[1972K20]

I've got a 72K5 that doesn't have air conditioning, so none of the AC components are currently there. Eventually, I will swap in a 5.3 w/AC and was wondering what AC parts I need from the 1972 setup to run AC with the 5.3 engine? I've never tried to setup AC before, so I'm not sure what all I'd need to make it work on a truck that never had it. I don't want to start buying original ACs parts when they may not be necessary. Thanks