So many folks are looking for a method to adapt 650B wheels to their rim brake 26" MTB frames. Some people have found the FMF V-Brakes to solve their adapter issues. The FMF brakes have additional brake pad adjustment to accommodate the larger rim diameter and brake track. Alas, FMF has discontinued all bicycle componentry just after this realization was made. There are some still floating in the interwebs, it will just take searching! The Paul Moto-Lite v-brakes have a similar solution with extra pad adjustment. Both of these, along with any other linear pull brakes, leave the inner cable crossing the tire VERY close. Physically moving the actual brake posts, AKA canti studs, is a solution I am taking with my Trek project. I cut off the exsisting studs and replaced them 15mm further from the dropout.
It looks as if I was a little over zealous with my torch. Recently released were these nifty little adapters originally intended for BMX bikes. At 11 and 12 bmxers are quickly growing and usually in between sizes. These adapter were designed to allow the use of J/Expert BMX wheels on Pro sized frames. That may be gibberish to some of you, but these will lend themselves nicely for 650B adaptation of 26" rim-braked frames. I'll be order these for resale shortly. Check back very soon!