You will want to look at the BB cups to see what they are marked. Peugeots up to about 1982 will probably be metric, so a BB cup marked 35x1; after that year, look for cups marked 1.37 x 24 TPI or something similar. If the latter, no big deal and modern parts should fit just fine. If it's metric gauge and threaded, so long as your headset and bottom bracket are in good shape and can be rebuilt, you're still okay. You mainly need to worry about the top half of the headset and the BB cups; bearings and spindles can be replaced, or if still reusable, just take off the big ring and used single chainring bolts and use the small ring in the inner position. It'll line up fine. On the headset, it's usually the bottom that wears out, and you can do what I did with a Swiss/French threaded bike and run a cleaned up old French top half with the crown race, lower cup and bearings from a basic Tange headset. It works beautifully.

If it's an 80s bike with an ATAX stem with allen key fittings, you should be fine. The infamous "Death Stem" Peugeot used was the AVA, a cast hollow aluminum unit with hex bolts used in the 60s and early 70s. Combined with AVA bars, which were flimsy and tended to droop on the ends after a few years, they were an accident waiting to happen.

Is there a tubing decal? Do you have Carbolite 103, which is a pretty basic mild steel, or some variant of Vitus or Reynolds tubing?