So, one reason I pointed you at orthonormal's sequence is that if you read all those posts they seem likely to trigger different intuitions for you.

I would also ask if you think that Aristotle - had he only been smarter - could have figured out his "unique type of physico-chemical causal (space-time) structure" from pure introspection. A negative answer would not automatically prove functionalism. We know of other limits on knowledge. But it does show that the thought experiment in which you are currently a simulation is at least as 'conceivable' as the thought experiment of a zombie without consciousness and perhaps even your scenarios. Furthermore, the mathematical examples of limits on self-knowledge actually point towards structure being independent of 'substrates'. That's how computer science started in the first place.