If you want to replace a suspension fork with a rigid one, you have to buy one specifically made for that purpose. Suspension forks are taller to allow for the travel, and the frames are built around that. If you replace your 65mm travel fork with a standard fork, the front of the frame will be lowered by that amount.

You'll need to replace your fork with one what has a similar axle to fork crown distance, with the cantilever brake braze-ons at the right height for your 700c or 26" wheel. Most of these are for threadless headsets, so you'll need to replace the headset and h-bar stem also. Viscious Cycles is one maker of these types of forks and their site describes how to measure and get the right fork.