If the bike had drop bars, there were adjusters on the Mafac levers. If it had upright bars, there were no adjusting barrels at all.

Don't lose those Mafac end ferrules!

The Motobecane crank should work if you use the spindle and cups from the Motobecane. That's assuming that the cups are French. Motobecane switched to Swiss threads before Peugeot did.

Good luck removing those fixed cups!