G grind cam and compression bump via 10:1 pistons are easy starting points. The throttle body on later cars is bigger too, but that is awfully obvious for a cheater move. After that the only fruitful area would be head work.
I don't have part numbers, but those are the likely moves. Also likely are larger front bearings/hubs.
The G grind cam actually gets it's name from the G cast into it:
Most all parts on a VW have a part number cast onto them, even the wiring connectors and little rubber plugs, there should be one cast onto the TB as well.
That's all good info there, after removing the TB you should be able to tell if the intake has been modified, or even easier if they used the FOX intake. Also measure the secondary throttle plate, easy.