Don't know if your Montagna frame is the same company that built my Montagna frame; and like you, I've not found any info whatsoever on mine.
Here are a few pics for your comparison, namely head badge and downtube logo....
Overall:
Headbadge:
Rear U-brake:
Funky bottom bracket:
Mine is made of Tange MTB double butted steel, seat tube is ovalized at the BB, and the rear end is really compact, presumably for stiffer, shorter, and therefore better climbing carachteristics.
The whole shebang is Tig welded and appears to be well made.
Interested to see pics of yours...