Can you post the ASTM B298 standard?
Probably not, it is something you have to buy. However, when I Google for it, I get a link like this:
http://www.astm.org/Standards/B298.htm And the abstract we get for free seems to have nothing to do with sodium polysulfide. I don't even see how poly sulfide is applicable to The Standard Specification for Silver-Coated Soft or Annealed Copper Wire.
I didn't even know it was possible to dissolve sulfur in NaOH. I'd have thought someone would have mentioned it before when people ask what sulfur is soluble in, even though this isn't actually a solution. Is it really that simple to make? Seems to me like it sould only exist at high temperatures and under pressure.
As to the real question, how you make solutions according to specific gravity, I suppose you'd just use repeated trial and error to get it in the range you want? But does that work -- you make a solution of sodium polysulfide and it can be diluted to any level.? Will it not decompose and drop the sulfur out at some point?