The lightest brakes that were in use in the early '70's were the lowly Weinmann 500. You would see them all over the place at time trials and in the pages of International Cycle Sport magazine. Some of us actually reshaped them ourselves during the "drillium era." I filed, drilled, and shaped one for my TT bike that weighed just over one ounce without pads, but it snapped in half when I installed the cable and pre-stretched it... Oops!
Mark (TT's are cool, 'cause you don't have to use brakes much) Ritz Foggy Arcata, CA http://www.kinetic-koffee.com