There are actually many differences, besides the triangular cut-out in the caliper arm. In fact, just about everything. Here's a pic (link is really long). I believe these are from about '73.
Or
Album of my Charles Martin with lots of early DA bit here:
http://www.imagestation.com/
Wayne Bingham
Falls Church VA
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Weren´t those DA brakes second generation after the ones w/o the "triangle"?
kim Klakow<<<<
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a set of the VERY rare Dura-Ace Side pull brakes, first generation, with levers and even ... Good hoods.
Mark Petry<<<<