^+1 The rifling in the SLX seat tube is easier to feel than see. And...the little leaf-shaped gussets with the "GPT" engravings that flank the joint between the seat tube and the BB shell (best seen in your second photo) are another Montello hallmark.
The caps of the seat stays at the joints with the seat lug look right also.
You have yourself the genuine article. Whatever it costs you to repaint it, it's worth it.