I'm in the process of a 650b conversion on a Schwinn Tempo. I'm using the rims mentioned earlier in the thread from e-bay seller uglyrm and the Tektro long reach brakes. I alxso have a 3x9 drivetrain with bar ends. I'm out of town on business right now, this is the only picture I have, but I've put a set of Pari Moto 38's on there and they look and fit fine. haven't had a chance to ride this one yet, but looking forward to getting home and taking it for a spin.
I love the saddle on the bike. This bike just looks comfy. I'll be curious to hear about the ride quality as well as the quality of those inexpensive 650b wheels.