I just noticed we were doing the same thing, only I was creating an anamorphic image, original black bars included. Which is something you don't want to do, I know now. 324*1.33=432 and 432*1.33=576 you see? We were just thinking in different directions.
I don't apply the same script on the whole movie btw, because of the vertical shifts. My DVD versions don't have them.