"Baked" painting processes at the assembly are more than likely completely different than what we can reproduce in the field. Using the photograph of the Falcon (cut from the film "The Rouge"), we can see the jam areas of the trunk do not yet have body color on them, yet we also know that there would be no way of getting complete coverage onto the jam area if the trunk were to be tied down as pictured. This being said to say that, going by this image, it would almost indicate the top of the deck lid up through the package tray, would be shot first, trunk opened and then inside the trunk and quarters, taillight panel next, (possibly tie the trunk down again?) and move forward down the sides & top of the car next.
Keep in mind that this whole process took a worker (more likely two workers) only about two minutes to shoot the whole car, then it actually went into the oven within a few more minutes (I'd say like 5 minutes total, start spray to entering the oven), this would include a few minutes for possibly another set of eyes to view the quality (touch up if needed) before getting baked where the oven baking process would flow out any "fogging" that might have occured with any overspray and/or touchups. (I agree with Jeff, likely they popped the trunk open again as part of the inspection process before getting baked)
IMHO, we simply cannot shoot a car with a garden hose style spray gun and get it to an oven as fast as these workers did PERIOD. Trying to "exact the process" to me seems like a mute point. Understanding how it was done in the day is one thing but in reality, trying to duplicate the results is the best we can hope for.
Materials used to paint a car these days and the environments individually available to any of us out here in the "real world" simply put, prevent us from doing it the "same way".