I believe the 1,242cc engines and the 1.4s share the same iron block. (But different bore/stroke.) However, since the heads are completely different you can't just swap in a 16v head and use the manifolds or electrics. You'd need a 16v wiring loom and ECU. If you wanted the 16v turbo'd that would take a lot of work, either a turbo kit or adapt the GT's system to suit. You'd also need to CC the cylinders and the head and check compression ratios.
But not a simple straight swap.