Hi Bo,
The pearl rings that you posted pics of could be pearls from lake Biwa and the organic flowing look of the rings is certainly from the right time period, but then they may not be as well. The problem with pearls from Lake Biwa is they don't look that different from some Chinese keishi. The "stick" pearls from China are what most people think of as Biwa because the dealers call them that. The Biwas that I used in the 1970's and early eighties came in different shapes, not just the long stick shapes.
IMO unless you have provenience on pearls being sold as Lake Biwa production it is difficult to impossible in most cases to tell the difference between them and Chinese production. Some of the Chinese "exotic" colors and some of the extreme orient and lustre on Chinese Keishi I never saw in the Biwa Pearls I handled.

My wife has a couple of pieces of jewelry with pearls from Lake Biwa in them that I will try to put pics up of today.

DFrey