@Jonny69
Yeah, I did put "madness" in the title
- 27.0 race instead of 26.6 ISO
- 25x1 French thread - confirmed
- 25.0 French steerer instead of 25.4 ISO
- 30.2 cups in line with ISO. [JIS that comes with 27.0 races has 30.0 so I was investigating using a JIS headset]
- 22.0 French quill instead of 22.2
- Stack height about 36mm. I originally thought 37, but that was being optimistic. Some French bikes supposedly come with as low as 33 (!).
Options:
1) Find some original prehistoric French headset that's a perfect match, is serviceable condition & at affordable price.
2) If can find a French Tange Levin headset in serviceable condition, the bottom race can be replaced with a modern Tange JIS one with no compatibility issues.
3) If you're not afraid to combine parts of different headsets in the same cup [generally, believed to be a very bad idea], there are options to combine the aforementioned JIS race with a different cup.
4) Run EC30 threadless via one of the hacks.