It is a Meisterstück 144 (or possibly 146; size measurement gives clarity) from the 1950s. The gold overlay is a sleeve that comes not from Montblanc itself but from goldsmiths in Pforzheim/Mühlacker — named are Bossert & Erhard, who still work for Montblanc today, and Sarastro as a maker of pocket-use articles. A hallmark indicates that it is indeed precious metal. The pen, despite the aftermarket overlay, is collectible and has relevant material value; inscriptions like 'Meisterstück' the old 144s did not necessarily carry.
Related pages on fountainpen.de:
• Montblanc Meisterstück 144 (Classique predecessor): https://www.fountainpen.de/c-montblanc-meisterstueck-144-en.htm