Thanks to excellent service from STW’er althepal, getting the matchmakers into the post quick sharp I have an answer.
Basically the Race lever match makers work with the old mini/mono mini levers. The only thing I had to do to get a robust set up was to change the bolts from M5x10 to M5x15 to get enough thread engagement as the race clamp is slightly thicker and leaves a slightly larger gap between the lever and clamp when bolted up. Obviously the profile of the clamp is different, but it doesn’t seem to stand out too much.
The bolt spacing is identical – thanks Hope! Still not convinced on the design of the X-fusion seat release mind….
N.