I built up this late-60s or early-70s, French-made, Dynamax as a singlespeed for a local customer. He brought me the bike, told me what he wanted, and I took it from there.
Alloy wheels (27"), square taper bottom bracket and crankset (to replace the cottered originals), and flipped bars pretty much remade the bike.
The bottom bracket, oddly enough, was British-thread rather than French. That simplified things a bit.
I also laced up the Ideale seat, in an effort to save it from the trash. The leather is overly soft, as if it's been treated with too much oil or something, yet the skirts were flared like it was dry. I laced it and adjusted the tension nut. Only time will tell if the leather will hold up to use.
The extension on the top of the handlebar is a mount for the generator-powered headlight.
I can't find any info on the Dynamax brand. The frame looks like a Motobecane, but that really doesn't mean anything. Steel tubes and Nervex lugs look the same, no matter who connected them. Plus, I've never seen a Motobecane of this vintage with a British bb shell.