Maul being Grievous gives Grievous some depth, and makes him not so much of a throwaway character. It would also show that Palpatine has a history of resurrecting his apprentices and putting them in mechanical suits.
I think Dooku actually works better as a tragic figure who is misled, instead of a genuine Sith apprentice.
But when it comes to making all this happen in an edit of Episode III, I have serious doubts that something can be done in a convincing matter.