It appears this watch comes from South America, presumably Argentina or Uruguay where those GP watches seem to have more current market than the time they were actually made.
To begin with the movement, that's all legit and in pretty good shape but it stops pretty much there. The case is certainly not the common size for the era and the hallmarks are not Swiss, suggesting it did not leave the factory in Switzerland together with the movement. That however, is still common as import taxes on precious metals led to local case production in many countries. But I would check with a jeweler if it is indeed 18K as hallmarked. The dial is a redial done pretty decently and the crown is clearly a newer replacement. You can certainly call this a GP although pretty 'worked on' GP.
As for the automatic wind caliber discussions - The 17 vs 39 jewels - These were both available from GP ..and from BENRUS under two jewel settiong options.
They even shared the same 'logo' for the 39 jewels (!).