OK new guy here with my first question. My 74 C10 originally had air conditioning. But when I bought it the prior owner had removed everything. Ducts, inside & outside heater boxes, heater controls, etc. and blocked off the firewall with sheet metal riveted over the holes. I would like to put a heater in but don't care about having A/C. What mods do I need to do to install non-A/C stuff ? Anyone have a picture of the firewall from under the hood with the heater box removed so I can see what's different ? I do have access to a non-A/C parts truck. Thanks.