Same here.
I also live a similar life every day at work. The weather or unreliable suppliers do affect production schedules unless you plan on carrying inventory far in excess of what is normally necessary. Weather would be considered a minor hiccup and generally shouldn't interupt production but occassionally it does in the case of flooding or major snowstorms.
I was just using the GT500 as an example. You could compare a GT to a Mazda6 or a V6 Mustang to a Mazda6 or any other model. The models are so different they can't have the same assembly content (and time required to perform the task) across all the different models.
We have 2011 Mustangs at our local dealer in all three flavors: V6, GT and GT500. That is, unless they are listing things on their website that they don't actually have on hand.
The plant is likely just a welding (main body structure only), paint and assembly plant. I've never been to that plant before but I would imagine that's how it is set up, all the subassemblies and components coming from other Ford plants or suppliers.
I didn't realize Ford sold the plant to Mazda and repurchased half of it, thanks for the lesson.