Converted Grand Banks
The current issue of Soundings has a article on a 1966 Grand Banks 36 that had a ketch rig added. The owners transit with one engine running and report substantial fuel savings, plus report the overall ride feels remarkably "normal".
They did add 7 inches to the keel an extend the rudders 14 inches to address . Quoting the article ".. the boat cruises as if it were designed for the modification and was only waiting for someone o figure it out".
It certainly is an out-of-the-box concept, but appears to be well executed. I couldn't find anything online, although I imagine stuff will appear eventually. Certainly not everyone's cup of tea, but seems to embody the 20/80 (or is it 80/20) tradeoff.