It will not work. The Mafac bosses are smaller in diameter and in a different position. The Paul's use contemporary standard canti bosses, the mafacs would have to have those same bosses turned down to a smaller size.
As an owner of both types of breaks, and a mechanic who has had to work many mafacs, the mafacs are a fine way to go if: you are not doing loaded touring, if you have a few sets as spares, and if you dont lust after the crispest braking action ever.
Set them up with new housing, clean them, make sure they arent bent up and rubbing on themselves, and put some salmon coloured kool stop pads on, and you are set.
The Pauls are nice, but actually heavier, so, go figure.