Hello JFerg,
I had a chat with Bosch (Australia) about this very thing when looking for Villiers replacement capacitors.
They advised that,
All Lucas capacitors are .25 microfarad,
All Bosch capacitors are .22 microfarad as are all Japanese ignition systems. Bosch stuff is built to the same standards as the Japanese.
They further advised that condensers and coils are designed to complement one another but they would expect a mix'n'match of the different makes to work okay although not as trustworthy as it could be.
The shape and dimensions of capacitors varied to suit engine makers demands but the electrical capacity always remained the same regardless. In short, any Lucas capacitor you can fit inside the end cover will be electrically correct.
To finish off, my original concern was about the Villiers capacitor. This is a .18 microfarad jobbie of which Bosch looked down their nose and advised was "rather marginal" (as if we didn't know that) but any of their capacitors could replace it. They particularly suggested their type GD9 as it had a useful mounting tag and a long pigtail wire so was easy to mount on the Villiers backplate and then run the wire through to the points. This is what I now have mounted on my Excelsior.
Cheers,