Based on the cap rings and what I found thru https://parkerpens.net/duovac.html I'm thinking a junior. The nib sizes out at 25.4mm long from tail to tip, 6.8mm at the shoulder, 5mm wide at the tail, 2.3mm height (measured the curvature). Using a digital caliper.
Seems to match closely to an identically inscribed nib on fivestarpens as "Parker Pen, Medium & firm, larger version of this nib, 26.5mm x 6.8mm, $34" (since there's a whole section of just "Parker Pen" inscriptions). Most of the others are a little shorter and slightly narrower on the shoulder.
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