I show the heater in the picture here. The 2 copper pipes that look like they'll run through the fire wall holes shown under the battery tray. The picture showing the firewall shows the heater hoses just connected together with a pipe near the two firewall holes. The fellow at the radiator shop that rehabbed the heater core said there may be a valve of some kind that would be attached to this core.
Attachments
gmc heater.JPG (257.94 KB, 102 downloads)
engine side firewall.JPG (188.4 KB, 102 downloads)