Does he need the outer dimensions, or is he just looking for the throat diameter?
If it's the latter, then Google around on "control line venturi size". Basically you're looking to make a venturi whose open area is a certain proportion of the engine displacement (and I can't remember the number!!!) after you've taken the size of the spraybar into account.
If it's the former, and you have the RC carb, can you send him that?