What is the offset on the wheels ? if they are 911 fronts they should be ET52 so with the hubcentric adaptors/spacers the offset should be right.
The rears should fill up the arches if they ate the wider 10x18.
I'm not sure how they will suit the car, which Turbo style are they ?
Depends on the offset of the wheels and taking into account the size of the pcd adaptors, the rears are not such a problem as there is quite a bit of room but you could have fouling problems on the front using full lock.
Personaly after thinking about them i don't think they will look right on a Gtv.
I have had a few customers with VW Golfs and Audi A3 / A4's with them on and they only just look ok as the Audi S2 with the old style 968 Club Sport wheels fitted if they have the larger 4pot brake callipers.
But on a Gtv it would just look wrong.
Every time i see an Alfa Romeo, i raise my hat.
Whenever i see the front of a Gtv i become sexually aroused.