What I've done in cases like this was to remove the cantilever posts and fork dropouts, cut 20mm off the fork-blades and re-installed the dropouts. Bent the fork over a mandrel to restore rake to about 80% of the original amount (not as much needed due to steeper head-angle).
For the rear, I removed the cantilever posts as well and installed a new brake-bridge 15mm lower for the 700c wheels and short-reach brakes. Also required new paint as well.