Charlie Baker's "Building the Really Right Inline" states that the 216/235 rod design, specifically the small end "pinch bolt" style, is a weak link for a motor turning high RPM on a regular basis. He speaks more of the pinch bolt or wristpin journal itself being prone to breaking under stress and notes that the 261 rod was beefed up considerably. Supposedly the 235 Corvette rods had this improvement too.