...I don't think those saddles were around when the Nervex lugged PX-10's were being made, but otherwise all that stuff looks authentic, even if it's not all original to that particular bike. The stem looks like one of the more solid ones you see on PX-10's of that era, so that's a plus. Mostly, they are a little idiosyncratic in threading (as already stated) and in the metric frame tubing diameters.
If you need to pull the crank arms, it's larger than the current standard puller diameter for that crank.
Here's one I have, that has some modifications to make it more of a rider, like clincher rims and a water bottle cage moved to the bars.
Amazon France and Ebay in France are some good places to look for parts, but it looks like you don't need many.