There's one of the original mid 70s boxed sets of Reynolds 531SL tubing on eBay.
The picture of the tubes shows the wheel clearance flat pressed into the chain stay. I've never seen this feature on any other style of Reynolds tubing.
http://search.bikelist.org/
The seller says that the tubing is "Imperial" (inch) size and and the decals are in English and that he received the set new from Proteus Design back in the day in the French box.
I bought 2 boxed sets of 531SL back in 1976. I built someone a frame with one set and saved the other for a frame for myself. I never got around to that project and sold the set along with most of my other frame building supplies to a current CR member about 10 years ago.
Now I wish I had that stuff back... ;-(
The fork blades in these sets had an ungraceful bend about 2/3rds from the bottom. I remember it was a bear reshaping them into a more attractive curve.
Chas. Colerich
Oakland, CA USA