Anyone ever replace lowest four tenor plain wire trichords with wound bichords? Will the new GH1 bichords work for those notes or do I have to custom measure?

I have replaced the lowest six notes with bichords supplied by Yamaha. It involves changing agraffes and adding hitch pins. You should contact Yamaha to see if they still offer the same kit for doing this as they once did and if not, if they have the specifications. It is a good solution. The piano will stay much better in tune in that area and the tone will also be improved.