have never seen an azimuth scale on an AI, though I believe the drift representation is linear. I haven't found what 'full-scale deflection' is
On the '320 family,there is indeed an azimuth scale on the AI,matching the heading scale below.
The drift is directly read against that scale exactly like the flight path angle is read against the pitch scale on the ADI.
Therefore the drift max deflection is 25 degrees,reducing somewhat at pitch angles greater than 10 degrees up or down,due to the curve of the attitude indicator.