what you had were "sewups" AKA tubulars, tubbies and sprints and the tires are glued onto the rim (or nowadays you can use Tufo double-stick tape instead of glue).
Are we seeing a crimp in the backside of the seat-tube to allow for tight rear tire clearance?
For some reason I think the old example with a similar forkcrown "S" was once ID'd as an Austrian brand "Simplon", but I also think that ID was shot down and a different positive ID was eventually made, but I would have to do a deep search of archives to find the old thread...
Look into the base of the fork's steerer and see if there are 5 shallow spiraling ridges in the metal...cause I'm guessing this might be Columbus SL tubing and not Reynolds 531.
Any markings on the dropouts or forkends such as: Campagnolo or Gipiemme or Columbus?