CRs:
Thank you all for the interest in my Mercian, and the nice discussion of the Phil Wood bottom bracket and the related issue of cranks and clearances.
The exposed axle taper on the Phil Wood bottom bracket is a quirk of how they machine the axle. The overall axle length is 113 mm, which matches the Campy spec. The 42 chainring clearance to the chainstay is slightly larger than typical because of the slightly deeper fluting on the right chainstay. However, both of the crank arms clear the chainstays by only 3 mm or 4 mm; I wouldn't want to go any tighter than this. The crank arms are not on the axle all the way, by any means.
Andrew Gillis
Long Beach, CA USA