Wow, thanks for all the details. In the meantime I also found a pdf on the conversion here. At first, though, I thought that the conversion increased the gear range, but now I see that this is to reduce gear spacing. Right?

I sort of can live with the gear spacing on a 6-speed but my concern is in the low gears. Some places I might take the Brompton to have tough long ascents. At the same time I don't want to lose the pleasure of overtaking racers on road bikes while riding a loaded Brompton. Yes, after they wake up the Nature usually goes back to normal but then I already saw the look on their face .

I have tons of cogs and spacers so am half way there, but with the gear range, I should presumably start with a second chainring. Even for this, I must first cope with at least some of the backlog in the projects...

P.S. There some Ti Parts Workshop conversion kit floating around for some incredible amount of $$$