Update: I wrote to Orbea redirecting to this thread, as many photos were present.
I had an email communication, which ended with them asking for a 11 characters serial number, which is present on any Orbea bike produced after 2008, to which I replied that this bicycle has been clearly made before 2008 and the frame is totally blank, maybe if they had somebody in their factory who is old enough they may have been able to identify it. But I then got the final message saying - we are sorry we can't help you further.
So, I decided with the time to paint it more or less like this one which is very similar in shape and particulars ban the rear brake cable passing inside the top tube. But with white bar tape.
I think I'll go for it being an Orbea, it's relatively easy finding decals over here, it's similar enough, it's local... And I obviously like it.
And then I got hooked by
this thread, so I think a Ergo transformation may occur, for an improved ride (many hills down here, gears are necessary and in this way aren't exactly comfortable)
non-fixie be reassured that when I do transformations on old vehicles (being these bicycles, but also on cars or motorbikes) I never do irreversible stuff, and I always try to keep what I took off, as it doesn't cost anything.