...this topic has some other threads you should read through.
https://www.google.com/search?q=rale...w=1048&bih=787
This one is relatively recent and has some information that might help you.
These bikes are surprisingly uncommon. Of all the mixte frames I saw move through the co-op here over a 6 year period, only one was a butted Reynolds 531 frame. It was a Raleigh product. Good luck.