Custom Oak Cycles 650B French Randonneur Project.

Some French 650b bikes especially tandems had lugged BBs with widely angled ports so that curved chainstays could be used to bring a big tyre and mudguard in tight and allow short chainstays with no dimples. I've seen a pic somewhere (Bicycle Quarterly probably) which shows a rear triangle without the wheel it's pretty cool.

Another notable example is the recent Rene Herse that have a custom bottom bracket to be able to accept larger tyres and mudguard, scroll down a bit to see it;

http://www.renehersebicycles.com/650b%20Herse.htm

Custom bottom bracket shell;

http://www.renehersebicycles.com/IMG_1591.JPG

Mudguard and tyres clearance are ample with a sight dimple, very important if the wheel gone out of true during a long Audax;

http://www.renehersebicycles.com/IMG_1615.JPG