Have I asked a really stupid question or something
The problem is that in fact tyre height/width is not an exact science, not only are they different for different make and model (despite having the same spec norminally), they can even change quite a bit with pressure - I had a Giant xtc which could take a Conti 2.3 at the back only if the tyre pressure was low.
The best I can suggest is
this (some dimensions at the bottom of the page, albeit it is not the exact same model) and
this for cross reference.
With 2.0 at the moment, I would have thought you shouldn't have any problem if you have 0.5" of clearance all round at present, or are you much much closer than that?