After seeing the Photoshop picture mate, I think they look awful sorry,
They look decent on the Subaru, but stick them on the Alfa and they look like any other generic ill fitting after market alloy wheel. They just don't go with the car whatsoever.
16" Teledials would look HEAPS better in my opinion, and they would actually suit the car, as opposed to the Scoobs wheels.
A member on here, Magicsy, had an Amazon Green 156 and stuck a set of 17" 166 Tele's on his car, they looked brilliant! Can't you go for something similar???
Your colour is my favourite 156 colour. If it has black leather as well then it's the piere de resistance in automotive styling,
If not then not to worry, you can get it fitted,
But yeah, please don't do it mate, it WILL look naff,