Brian, the heater core tubes are already clear of the firewall. On mine, the hoses came through the firewall and clamped onto the tubes inside the cab.
I did some more looking around, and there appears to be a door of some kind opening into the louvered section of the outer cowl. In fact, the control cable I disconnected looks like it might control that door. However, I can't get it to budge. It is probably rusted up tight. Maybe if I start gently beating on it with a rubber hammer???
