I think you are missing something obvious here. Pain does not exist in any objective sense, it is a construct created by the brain in response to certain stimuli as a survival mechanism. If you were creating a simulation of a human body to use in medical experiments then surely you would not give it a brain that functioned in any meaningful sense.

I would not say that a body incapable of feeling pain is an "inadequate replica". A human or animal under anaesthetic does not feel pain - are they inadequate. You can certainly perform surgery on an unconscious person, and you can administer medications to them.

[edit] I should have added that I am totally in agreement that we are not even close to being able to simulate a human body with any degree of accuracy.