Sheldon Brown's site says 24 x 1&3/8 used on wheelchairs is 540mm,
"French 600A is actually 541 mm, close enough".
I notice the frame (just behind the head) has a hole or lug to take a cable, I guess some of these had gears. I assume the rear brake cable is in through the other side. Yes indeed, it is a tres beau velo, solide...