The parts books were very detailed on this, giving the weight of dozens of options that only weighed 2 or 3 pounds for earlier years. In 1979, though, you are supposed to get GAWRF from the sticker on the left door and go by that. I don't even know what GAWRF stands for.
For 1979 WS6, they used just two part numbers, 482509 (light) and 3988113 (heavy = above 953 kgs). This was for service, and they might have had more to pick from on the assembly line. I'm not sure, but we could certainly figure it out from looking at 1979 WS6 build sheets.
I don't know if there is a way to convert starting from these part numbers.
These springs were widely used. Brian Morelock told me 30 years ago that he had a 1977 Oldsmobile Cutlass Supreme, and he went to put WS6 springs under it, but the springs were tagged, and it already had the same springs.