Welcome to the forum Corrado
I am sorry that it takes someone with better knowledge (than me) to distinguish a Portuguese lock from a Spanish one. There are lots of similarities and often experts use the term "Portuguese (patilha) lock in the Castillian style".
You can also see this type of stock in both countries.
For some, the fixing of the parts with (plenty small) brass nails means Spain (Ripoll); but is also wide spread that, the position of the screw that fixes the barrel to the stock being in the inverted position, like in your example, means Portuguese.
We may also consider that having no marks or names tend to be Portuguese; Spanish examples were more often profusely marked.
It would be interesting to see a photo of the frizzen front face; is it plain or has any decoration ? Is the inner (striking) face removable ?
In any case this is a rather interesting pistol, Corrado; i wouldn't mind having it in my small collection