Actually that 12.5 x 13 prop is about 85% of the minimum load recommended for this engine.... So with good lubrication and ventilation... I'm betting on a midair or other "unfortunate end" to that airplane before the engine gives it up! Just a prediction. An 18x6 is about the equivalent in the other direction (overload/above spec)... wonder if that would cause a failure first under full throttle conditions or the smaller prop would?? Of course, I did say with adequate ventilation and lubrication... we don't know if that is happening or not!