The bleach is interchangeable (I believe, I know the processes use two different bleaches) fixer is, neither of the developers are interchangeable with acceptable results. The final rinses are interchangeable, but you still need the pre-bleach to achieve proper stability.
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
I would interchange only fixer. A traditional formalin-based stabilizer should also work in any process, be it "3-bath" E6, real E6 or C-41 with older and current films.