Some long reach brakes mounted in the rack hole and rear bridge ought to let you ride 700c and keep the canti posts intact. There’s probably plenty of dia compe centerpulls and the like at that bike recycling place.
Interesting thought, cheers. I better check the clearance for 700c in the first instance. 650b might be a better fit though I can't ever imagine buying rim brake 650b wheel to be honest. Would be fun to be able to fit any old wheel though, both rim and disk, 26", 650b or 700c.
Some long reach brakes mounted in the rack hole and rear bridge ought to let you ride 700c and keep the canti posts intact. There’s probably plenty of dia compe centerpulls and the like at that bike recycling place.