We are overlooking the many 100% Eroica-compliant dual pivot brakes that are out there. You know them as center pulls. MAFAC Racers and Competitions, Universal 61s, Weinmann 750s and the look-alike Dia Compes, to name some examples - they all have two pivots (and thus are dual pivot brakes), some work really well and most work acceptably well (Kool Stop pads, aero levers and modern cabling are your friends), they are readily available, and no one at Eroica will think twice about them.
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"I'm in shape -- round is a shape." Andy Rooney