I think including other parts of the body is the least of the problems. The bigger problem is that we don't understand how close to the structure of the brain (+ nervous system and gut and anything else contributing) we need to get for the simulated system to have a subjective experience of consciousness. E.g. is it enough to run a simulation on a normal computer? Does it need to process information at a certain rate to sustain this process? Is a certain physical structure of the simulating machinery required?

I don't agree we necessarily will be unable to reproduce it without being able to define consciousness, though, but I suspect we would agree that we won't be able to know if we have reproduced it or just created something very good at acting as if it's conscious (and we don't know whether or not the two are equivalent).