62 Starfire

Trying to figure out what it takes to get to the heater core on my '62 Starfire. Tried from the firewall side, no luck there, just made a mess out of all the vacuum lines. Tried to get to it from under the dash, and could not figure out how to get past the plastic ductwork. Do I have to pull the entire dashboard out? If so, how do I go about that without tearing anything up? Any help out there?