I believe, but am not certain, that frame is from this model:
http://www.classicrendezvous.com/Fra...Jeunet_630.htm
One of the oddities of this particular Jeunet frame is it has no integral derailleur hanger, unlike almost all other hi end French bikes of the time. I've seen a couple, and can vouch this is how they were stock.
The lack of 531 stickers is a concern for purposes of identification, but they're almost completely gone on a couple of my old Frenchies. So their lack isn't an entire worry. A lower end entry level bike would not have the Simplex drops. It's a decent frame, quite likely hand built, given the age.
The French threading is a minor pain. The lack of a BB concerns me, and although Sugino or Sakae still makes one, they're pricey (about 55$). You can reportedly use a BB for stripped BB shells; YST makes a sealed one for under 18$. You can still find French HS, but if you're going to run a French bike, I recommend some parts hoarding. You can also find used French parts, contact this citibikes to see if they have any.
French frames tend towards a very relaxed geometry and make comfortable urban fixies. There are a couple of exceptions to this geometry, notably most Gitanes and a few Peugeot PX variants.