26" MTB and 650B are not the same. A 650B is taller. I did the math for putting 26" wheels on an 80's Japanese road bike frame. The centerpull brakes recommended by Rivendell site would *barely be long enough. However, the crank would be lowered so much it was a no-go. By the way, this would have been an easy 650B conversion but MTB wheels are no-go. I just put a late 80's mountain bike into road service and I am very happy with the results. The biggest piece of work was converting from straight mountain handlebars to drop road bars. Everything had to be changed out (stem, handlebars, brake levers, brake cable hanger, shifters).

Bob