Brucey - thanks for the very helpful feedback on the BBs. I guess I will try the modern Campag Centaur BB in 111mm (English thread), sounds like this should be okay on a decent non-oversized Audax frame (e.g. Mercian) and there is no Chrous in 111mm.
Re: the brakes - I guess it's just because I see this mostly as a spring/summer bike, so need for permanent mudguards is perhaps less (though that's never a given in the UK...), if the weather looked really foul for a ride, I would probably go on the Cheviot instead, almost certainly in winter, which is setup as a fast tourer. But, it would certainly be nice to have the option of proper mudguards for audax-type rides even in summer, with British weather being so unpredictable.
Surely if specifying the frame/forks myself (e.g. to Mercian), though, there would be some scope to set a requirement for clearance for 25mm tyres and mudguards with 50mm (or perhaps 52mm) drop? Or am I living in dreamland
Would using Aican offset brake shoes in extremis be viable to try to extend the reach, or are they just a bad idea (bit ugly for a start...)?:
https://www.ebay.co.uk/itm/AICAN-Aluminum-C-Brake-Shoes-for-fit-Mini-Velos-smal-Shimano-Sram-1-Pair/252782117509BTW some of the photos I've seen of the BR-R650s seem to show them more as a flat anodised greyish silver, rather than a more polished-looking silver - are there two types?