It looks like your brake bridge and fork crown have plenty of clearance for the extra 13mm. Check the chainstay bridge as well. Then the only other issue that I can think of would be your cantilever brakes, and whether they have enough vertical adjustment range to move the pads the additional 13mm higher.

I've never seen Campagnolo cantis!

Also, why would you want to switch to 650B? The most common reason is to be able to fit fat tires on a bike otherwise designed for 700c, without changing the geometry. If the bike was made for 650C, then the switch to 650B along with fatter tires would raise the bottom bracket significantly, as well as increase the front end trail.

What's the bottom bracket height as it is now? It looks low to me, although that could just be the camera angle.