Older Chameleon's don't have slotted disc tabs, and you can't use the V-brakes with a 650B wheel. If you used the adapters designed to allow a derailer, you could line up the brake, but I don't think there would be enough clearance for the larger tire.
Using a White Industries eccentric disc-brake adapter might make it possible, however.
With a 650B compatible fork, you could run one up front. I think the Chameleon geometry would work great with a larger front tire.
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