My early 70's UO8 is reynolds 531. If you do end up stripping all the paint like I did, mine was labeled "Reynolds 531" on the top tube right before it get to the lug attaching to the head tube.

Mine also has same headbadge and decals were pretty close. Mine has a Stronglight crank, which is a pain. I checked five LBS and none had the crank tool to remove a Stronglight as they use a 23.35mm puller and the "universal" tools don't work for it. If yours is a Stronglight there is a tool that you can buy online but its pretty pricey for such a simple job.

I love mine, but it was pretty frustrating dealing with vintage french stuff and mine was complete when I got it. I can't imagine your future headaches, haha. Enjoy it.