Most were cast at the Saginaw (part of GM's "Central Foundry Division") and Tonawanda foundries. The machining for the Saginaw cast heads was performed at the Flint Engine Assembly plant. Tonawanda had it's own machining facility.
You can find additional information here.
http://www.camaros.org/pdf/cast_codes.pdf
https://media.gm.com/media/us/en/gm/.../defiance.html