B.C. Miroku (Miroku Taiyo Zuki---180 Inari-Cho, Kochi-city Japan) : "Model 550 Side-By-Side is a box-lock Anson & Deeley type gun with treble bolting, double triggers, sliding safety, automatic ejectors, scroll engraved case hardened frame, straight French Walnut stock, finely checkered. Weight 6.6lbs." This info is ca. 1963.
Your Mod 500 is ***APPROVED FOR USE***
DB
NP: you have "less advanced" Mod. 500 EXTRACTOR gun.