Short answer I don't know
Also you don't say which type of T/B As the 1.2 60hp either had, cable or flyby wire
They run on different inlet manifolds and wiring
5519278 as fitted to 1.2 60 and 69hp and 1.4 LPG 78HP flyby wire
77363289 as fitted to 60 and 69hp cable
Seeing as fiat didn't increase the throttle size or change the manifolds when adding 15% to the top end, I not sure just changing the throttle body is going to achieve anything, by all means give it a try and report back
You will have to fit some sort of adaptor plate otherwise the step would harm airflow
Low end throttle modulation would also suffer
As far as I know there isn't a cheap bolt on upgrade such as air filters or exhaust that makes any noticeable difference, that not to say the engine isn't turntable, it is, just not cheap, which is why using the 1.4, loom and electronics, from a donor 100hp is more popular
Camshaft and head work is the normal starting place, also the 1.2 can be bored and stroked to increase its capacity to 1388