bummer, sorry for that setback. I am not a fire expert, albeit I have done some wire melting myself.
Do you have a rough idea what was the origin of the fire? That driver's side valve cover looks a bit cooked more than the rest.
As for the defrost/heat vacuum control the later series, 86 and newer relies on a vacuum module built behind the Heater/AC panel
here is the vacuum ball on the firewall
and the hvac unit, with the vacuum outlets, it is a module that has all the vacuum hoses attached to a white plastic block
and the top view -I had to go to the junkyard to practice removal-