I bought a few pairs of NIB Model 300, nickel/chained and can't find any info on them.
All I can find is a WTB post where they refer to them as "vintage" and an old eBay auction where they sold with a crusty old leather case for about $120!
I was just gonna use them for spares and/or bedroom use but if they're valuable I might leave them in the box! I thought the engraving on them looked a bit cheap, but it would sorta make sense that it's just old and therefore looks strange to me.