I am in agreement with
dddd on *almost* everything: couple of tips: I have had incredible luck (or maybe its just not a big problem) with SR quill stems fitting quite well into the standard Peugeot steerer tubes of this era - TBH as a young pup I didn't even know there were differences and my own AO-8 has had at least a half dozen different stems over the years and none of them were a problem; second point is that the seat post is easily replaced (again I have had good luck with several SR Laprade posts) *if* you take out the spacer from the frame. Can't tell from the photos but if your current seat post is not stepped where the seat clamp goes on be aware that even a tiny bit of looseness can result in the seat slowly sliding down the post and the end of the post eventually carving its way through the leather of the saddle (DAMHIK) and even potentially poking you where you probably don't want to be poked. Finally, I have not found the pedals on any of the cranks I have seen from this era of Peugeot to be anything other than 9/16 standard thread, again might be just anecdotal. You won't know until you try!
edit: just saw your update: I have used 6 speed on mine for decades.....
