This sounds like it could be fun but I would be VERY careful in Nuevo Leon. There have been literally thousands of kidnappings and murders by the narcos in the last couple years. It's really not a place you want to go. If there is some other way you can get to Puebla, I would STRONGLY recommend doing that instead.
Also I hope you called ahead to the plant in Mexico. They don't give tours unless you have an in with someone.