Stephen, the ad says he took them off his lightweight, so I'd think they
should fit a S3. I don't understand, "The flange is about central".
They're painted white, too. Personally, I'd give them a miss. Why not ask the seller via ebay.
You'd get a nice set of steel Mangels wheels for not much more, or even go for a set of 2nd hand Disco 1 wheels.
Geoff