Fine bikes: I've always had a soft spot (and respect) for these after working on a couple (not kept but sold on).
They are under-appreciated IMO, but that's to be expected because they are seldom seen.
Do you know if this frame is Columbus or Oria tubing, and what model tubing?

this one and only scan on Mark Bulgier's site shows frames (ribbed and indented) with 2 types of Oria tubing:

https://bulgier.net/pics/bike/Catalogs/Montagner/1.jpg