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@user87446
post #12 was from the original author to this article, not me.
I used a Dremel type of high speed hand held grinder to remove some material from the small cog. I sort-of chamfered it to allow the thickness of the original Brompton circlip to be installed, but not before I ground some material from the O.D. and a bit of the thickness of the circlip. I do not think grinding this clip compromises its strength. It is made of hardened spring steel, and its only purpose is to take up the space in the groove in the cassette body to keep the sprockets in place. Fitting the circlip is a trial and error application, but if you go (grind) slowly it will eventually fit and work fine.
I only shimmed the plastic chain tension mechanism out about 1 mm using two pieces cut from a plastic spiral notebook cover. No other modifications were necessary. You will have to adjust the two set screws on the chain pusher too. As far as removing material from the chain pusher wings: that may help a small bit, but this part is not very thick to begin with, so filing may weaken it. I have been riding with this set up regularly for the past few months, and it performs flawless.