I converted a1985 Univega Nuovo Sport. I have 35mm Col de la Vie tires and they fit, but not with a lot of cearance at the rear chain stays. Many Univegas and Miyatas from that era a good candidates as they have sufficient clearances for wide tires and fenders. Many of them also have a a high bottom bracket, so pedal to ground clearance isn't a problem.

I use old Weinmann 750 centerpulls because I had a pair, but I guess long reach Tektros sidepulls would also work.

As to the question Grand Bois raised as to wether there is any advantage of a 650B over a wide 700c tire if the bike canfit wide 700c tires, I would say that for smaller frames, there is, because the smaller wheels eliminate or reduce toe-fender overlap. Another plus for smaller frames is that they look better proportioned. At least to my eye.