Wow, you found one! An alternative is to fit the VDP parts to your Sovereign. They all fit, and can be easily sourced from Series 3 VDPs, Jaguar or Daimler. Here in the US, we never had Daimlers (due to an agreement between Jag and Daimler Benz). We thought that the S3 VDP option was original, not realizing that it was identical to that on the earlier Daimlers, from 1973.
If yours is a SWB, the only problems are fitting the shiny stainless tread plates (the rears must be cut down slightly) and fitting the rear door section of the chrome side finishers. They must be cut down, which would require brazing and rechroming in order to retain the molded ends.
See the thread below for photos of my VDP style door panels and rear seat.