As I have said, I have been looking at a lot of options for my little 1.2 in my Punto which is the 16V 85hp engine you can uprate the whole intake system and the exhaust. port and polish, new cams and remap the ECU, even after all that which would easily run into 4 figures, you would still only get just a little over 100hp as this is what other people have done. Its been proven, tried and tested.
The 8valve head here is going to be the main limiting factor. you could add a turbo but has been proven on this forum over the last 20 years a stock 1.2 engine tends to die extremely quickly once you add a turbo. They are just not reliable.
One member on here "Brin" managed 150ish HP out of a 1.2 8V Punto a few years back (maybe 10 or more now) by fitting a turbo, but the engine just destroyed itself repeatedly and he spent a fortune on that. one other Turbo punto I know of, that was discussed recently burnt to the ground when it caught fire.
Even at 150hp that is still not as much as a stock Grande Punto Abarth, and you could get 595 Abarth and tweek the boost for instant gains.