"Why are the 96 mm as opposed to the regular 100 by everyone else."

I have no idea. Some gallic inscrutibility, I suppose. I just deal with them as they come to me; in general, I've found it's not the hardest fix on an older French roadie. You might measure the distance between the fork dropouts when you get a chance, but every UO I've seen is at 96 up front.

One thing I forgot to address is the subject of the rear derailleur; Simplex derailleurs from this period were partially made of a plastic called Derlin. It's notorious for breakage, though I've never seen a rear go, just the front. It's very common to see older Peugeots with the rear mech changed out to a Suntour or something like. I have a pair of Px's I've kept the original Simplex derailleurs on ('67 and '72), though, and they've been fine (knock on wood). If you really want to show, a proper Simplex rear derailleur is not hard to find and can be relatively cheap.

It sounds to me like you're having fun with the bike, and that's what's ultimately important. Fix it up and ride it, I say. Older bikes are a realtively cheap hobby and very enjoyable.

Have fun!