That is really cool. I imagine finding replacement parts for the throw will be a challenge. A Sonor beer-tap style throw would look awesome as a replacement.

Test it with a magnet. I don't know if Sonor made aluminum shells back then, so if a magnet doesn't stick, it's probably brass. I really don't know much about Sonor, other than a few snares I've had over the years, which were ferro manganese shells. I'm guessing this one is brass, but maybe someone with more knowledge can weigh in. 

D-421. SONOR stopped putting the stopwatch throw on double lug snares in 65 or some 66, by 67 it went on single lug snares and became the D 424.  Weight determines brass or not, magnet tells Ferromanganese from COSteel. I doubt Ferro, because too early I think. The throw comes in plastic or metal. Nobody seems to be able to hang on to the cover. the cover is more rare than the snare. Oh, the double mallet logo badge belongs to it.

Checking back,

 I see stings I shouldn't.  Maybe made to look 424.