Looking more into my project to run cantilever brakes on my U-brake equipped GT Zaskar I've decided the best course of action is to buy some cantilever mounts from Nova and have a general welding shop take care of affixing them. That being the case I need to make sure I tell them to put them in the right place. Is there any guidelines for how to position cantilever pivots? I assume the critical dimensions are the width and distance from the axle, with the posts tangent to the rim as close as possible. Are there any books or guides that would cover this?
A general welder won't have a jig to keep the bosses in place and will probably overheat the seatstays. Take it to a framebuilder. You'll have to get it re-heat-treated and re-painted afterwards as well.
You sure you want to do this? U-brakes aren't that bad, and you can always use one of those "travel agent" things if you want to use a V-brake lever.
I seem to remember adapters that would mount to U-brake bosses that would allow cantilevers/V-brakes to be mounted to them. Made by Odyssey maybe? Might want to keep an eye out for one of those.