First obvious thing to check is the belt, but since you drove it awhile after getting the charge fault, you would have also overheated and noticed no power steering had you lost the belt, so I doubt that's it.
Check the torque and cleanliness on the battery terminals, and maybe have it (the battery) tested. An internally-shorted battery can cause very weird things to happen.
Removing the alternator and having it bench tested is next. It's kinda rare they just suddenly die like you experienced, but a diode shorting out isn't unheard of.
If the alt tests good, and since you recently installed headers, my gut suspicion would lie in the area of the two wires and fusible links at the starter that essentially connect the alternator to the positive battery terminal (the starter post is just used as a junction point where the three wires tie together).
Because these wires are in very close proximity to the header tubes, melting them can happen if care was not taken to orient them properly on the starter post, so that they don't touch or lie near the header tubes. If you toasted them or they are shorting out to something metal, you would definitely lose charging.
If it helps, here is the schematic for the charging system:
