I believe to refine the bleach question, E6 bleach, a stronger than c-41 bleach is fine on c-41, but c-41 bleach chemistry's action is not sufficiently active to bleach all required surplus dyes. I believe this is a side effect of slide film being colour former rich, while neg film is colour former starved. So e6 has more colur former dyes along with elemental silver that formed the image to bleach away