That's what I'm thinking. 531 tubes but not 531 stays and forks. No chrome on the stays. Some components downgraded as compared to the PX10. The seat post is 26.4 mm, which implies a butted tube, if I understand correctly. I've read that some PR10 tubes were butted, but not all. Doesn't really matter to me -- it's a pretty good early 70s mid-range frame and I like it.

Not sure what to make of the Mafac levers with the plastic "hoods." Look to be in very good shape with no damage. Just need to try them out and see.

Seems to be a bit bigger frame than I thought. Measures as 56 cm c-c. I was guessing 53 or 54. Tad big for me -- better get a catcher's cup.