These surfaces should be accurately machined at the factory, but they will have paint on them, which must be removed, at the minimum. If you've got a good local shop that you trust to do the facing properly, it won't hurt to have it done. I always carefully remove the paint and measure the surfaces myself. Neither of the C-40 frames I owned were in need of facing.
When using modern cranks like the Campy UT, the BB shell width must be held to 68mm + or - .8mm for the crank to work properly.
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