Without a picture, the exact assignment can hardly be made. Astoria, however, made alongside Safety models also lever fountain pens in different sizes, among others in size 1, partly also with overlay. A designation "Montblanc-Astoria" could not be clarified; for a reliable determination photos should be consulted.

Related pages on fountainpen.de:
• Astoria — brand overview (fountainpen.de): https://www.fountainpen.de/astoria-en.htm