I just purchased a bike that has no markings save for the 531 sticker on the seat tube...but it DOES seem to be built of 531 and likely about a 1980 build date, based on details and components. Seller had no clue about it, didn't know much more than it was "mostly Campy", which is true: virtually all NR except for the Shimano DuraAce crankset with humungous DynaDrive(?) pedals. My best guess it that it's American or British, the most distinctive feature is the fastback rear cluster and serial numbers on BB shell and back or steering column: 2318141. Hoping somebody can ID it based on that serial plus some really crappy pics (not mine) and fairly complete description on this Velospace page:http://velospace.org/node/1962 I will take better detail pics and post them to the same site ASAP...but meanwhile, any educated guesses?? Thanks in Advance, Alan Goldsworthy San Francisco, CA, USA