You need 280mm carriers also
This.
Been down Stag Lane then?

Early G3 GTIs have 280mm fronts IIRC. So hubs and calipers off the Seat, carriers off an early G3 GTI.
Check the diameter of the Seat brakes first though - they fitted bigger brakes to some of the later stuff - you *may* get lucky.
Don't forget to replace your master cylinder with a 22mm one, too.