BTW if anyone's interested, I have the Mavic tool for cutting the chamfer in the BB. I'll do the job for free if you bring me your frame. I think some other folks on this list have the tool too, JohnDThompson maybe?
Mine has been used only once. It was not a popular request.

Fun fact (?), replayed to me by our local Mavic rep, who was not an engineer so take it with a grain of salt but I tend to believe it. Unlike most cartridge-bearing BBs of the day, like OMAS and Stronglight who used an annular bearing, Mavic used angular-contact cartridges, so you can adjust out any axial or radial play. I think they were meant to run with a slight amount of preload, i.e. adjusted a tiny bit tighter than the "no play" point. The two cups that hold the bearings in are marked Fixe and Mobile (or something like that, not looking at one now), and you adjust the Mobile side.

Can anyone confirm or refute this no-so-reliable memory of mine?

EDIT: OK I think I refuted it myself. This document
https://www.disraeligears.co.uk/site...7_page_30.html
shows the bearings as deep-groove, not angular-contact. They do tell you how to adjust out any play, using the bearing cover marked Mobile, so that part of my memory was right.