Also a fan of Montagner cause I once owned one, true that both Scapin and Pinarello are better known marques but priced accordingly. assuming a build-up from bare frame is on the cards, only thing that might scare me off is that dark patch on the Montagner's downtube: it needs close inspection. The IRIDE is possibly more modern (has shorty semi-vertical DOs, could have a wider rear spacing) and it's a 54, but I'd check it out as well if the size is not off-putting. Never heard of IRIDE but wonder if this is a re-brand/re-paint of something else. This could be a "plus" tho, since you are talking of modern drivetrain on a more "C&V frame".
Per your questions of comparing the Scapin to the Monty: I do not know what this ATEC model would be built with but the fork blade seems to have the silver back decal that was common on Cromor bladed forks, so maybe the frame is Cromor, maybe better (like SL). Yes it DOES have a fair amount of chrome but Scapin was generous with the chrome, even on cheaper-grade tubesets like Zeta or Gara. And the workmanship was higher-tier than the tubing would warrant. The Monty might be Oria but if so I'd bet it's around Columbus SL, and in fact Montagner was using Columbus before switching to Oria so if you check it in person see if there's any remnant of tubing decal, and check the steerer's base for Columbus "rifling".