I pulled the heater. It looks like it has been out before. The grommets are missing and anti-seize was used on the mounting threads, the firewall was also a little bent. But the heater core itself looks great and I see no signs of previous leaks. Still, I will test it before putting it back in the car.
I'm not sure if the fan motor works. The external wiring is shot and I don't have a 6-volt battery or power supply. If it doesn't work there are probably shops in Sacramento that can rebuild it.