You've got the point as RoTechnics was the company name I was after, and you've added some useful additional information too.
As you say, two Ro80 Convertibles were made by Simon Kremer of RoTechnics before he sadly died at an young age in the mid-1990s. He had planed to make more Convertibles at his small workshop near Windsor in England, where he used to install the more reliable Mazda RX7 engines into Ro80.