Please no! IMHO It reduces the gap in the arch and it never looks as good as people think. Get Defender wings and a rear tub instead if you really need the width.
Right, the story is that the S3 he has purchased is a Re-Built thing. Its a rag top, with a 200TDI lump, RR axles front & back. It's in very good condition.
If ti has RR axles it will need the arch extensions as they will put the tyres sitting outside of the body work even with small offset wheels., but i agree with the above, none of then will really look right, they are difficult to retrofit well.
How about pushing out the wings like they used to do on the homogation rally cars! Cut a slit across the top and jack out, then rivet in a filler plate. Would be a one off. Could look pants or great, you (opps "he") wont know till he tries.