As others have pointed out, you postulate a difference between materially identical worlds, then conclude that these materially identical worlds are different thus dualism. Your conclusion is in your premises: a circular argument. — Kenosha Kid

No, it isn't. It is simple set theory.

You simply compare the set {A*,B,C,...,X,Y,Z} with the set {A,B,C,...,X,Y,Z*}, where the star indicates which life you would live in the corresponding world.
It is possible that the persons are materially identical in pairs, i.e. A* =(material) A, B =(material) B, ... , Y =(material) Y, Z =(material) Z*. So {A*,B,C,...,X,Y,Z} =(material) {A,B,C,...,X,Y,Z*}, but of course also {A*,B,C,...,X,Y,Z} <>(total) {A,B,C,...,X,Y,Z*}.

See it as a proof of contradiction.

As already mentioned, the worlds should not exist simultaneously, but alternatively. Thus the question does not arise "where" these worlds are.

A simple question: Would it make no difference to you whether you lead your current life or the life of another person, for example George Clooney, of course including his body and memories?

It is incredible how such a simple proof can be so misleading. Two ideas are compared. Can two ideas be identical or only the same? It does not matter.

The central assertion of my proof is: WA = WZ (physical), but WA <> WZ (total), therefore something unphysical must exist.

If these are parallel worlds that are identical, then they have the same "histories", and person A in one world would have the same memories and history as person A in the other world.

Of course they are identical. This is the core of the proof, it is not a bug, it is a feature.

More formal speaking you compare world A = ({A,B,C, ... ,X,Y,Z} living as A) with world Z = ({A,B,C, ... ,X,Y,Z} living as Z).

What about the space each world occupies? is it also identical for both worlds?

You compare two visions. They are not beside each other. They are alternatives. And they are not equal. It plays a role being one person or another. Don't you think so?