The ultimate tuning step on a Panda consists in swapping the FIRE 1.2 16v engine from Punto Sporting...it's a power of 86 or 80Hp due to the version!I think it can meet all your power request on a Panda without needing too many structural changes...of course I'll expect a servo brake system with more performing discs and pads...unfortunately is almost impossible to swap rear discs from other Fiats[xx(]!
The last possibility is to tune your 1.0 or 1.1 stock engine...the first one equipped with a new camshaft, lowered head, lightened flywheel and an enlarged throttle body (or Weber carb) can produce more than 60Hp from the original 45!