The calibre content server most definitely can be run in a headless environment without xvfb (I run it like that all the time). Furthermore, the calibre installation package comes bundled with all deps (except the X libraries), so it is trivial to set it up in a headless environment. Just install X (but dont start it) and then run the calibre install command.
But, I dont want to discourage you, feel free to work on a solution that suits your needs.
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