A/C to Heat ONLY conversion on 68 Dart Sports Special

Hello,
I am interested in putting heat in my car but I am not quite sure of what I need to do. I own a 68 dart sports special and it originally came with A/C. However, most of the A/C components have been torn out and I never plan to ever restore the A/C (at least for the foreseeable future). However, I do wish to have heat in the car to prevent fogged up windows and ice on those rare cold days. I am really not even sure about where to start with this conversion. Thank you for any help you guys can provide.