Watch out for interference with exposed cables on front cantilever brakes. Same hazard when mounting anything near canti brakes with exposed cables -- front bags, mounting lights or accessories on the head tube, etc.

I tried a similar arrangement on my Univega Via Carisma and gave it up pretty quickly. Switched to a weatherproof AGU bag from the Netherlands when Nashbar blew 'em out at $20, including the KlickFix mount. The mount allows about 3" of space, no risk of interfering with cables.

Or get some plastic tubing or a short length of cable housing to guard the moving front canti brake cable. Leave the tubing/housing about one inch short, enough to avoid interfering with full brake cable movement.