Chances are you could fit the whole lot to the Punto as there will be minimal difference between the models from a cost saving perspective, the whole reason for platform sharing.
Its a bit pointless for a couple of bhp, you'd probably need to do some work with the other computers too as I'd hazard a guess that the communications are coded and expect to speak to a particular ID.
Do what others do and fit a TMC or something, cheaper and easier, blimey you could probably get 5bhp by an exhaust or air filter, perhaps look at a new IC but swapping to Mito ECU pretty pointless.
Considering the number of 170s I see in the engine bay I'd be surprised if there was much difference between them at all just marketing, I know a few years back we had a dyno day and tested a 140 147 and 150bhp GT JTD both cars put out ~148bhp.
