The original GT and G40 radiators were dimensionally the same as any other Polo (*except some European spec. and diesel models) but had a denser core for better cooling.
I'm pretty sure they are obsolete now from VW. However, whilst not as efficient as a new OE one many people use new base model ones without problem - these are still available from some motor factors/ebay etc.
If you are running a high power engine and/or do a lot of track days you may want to get an ally radiator. These are pretty expensive though.