Its hard but it seems like your sorting it out the right way. In my case I had a pretty good idea from the dyno and drag strip of the acceptable high rpm timing. I assume you have that or are going by the MP guidelines of 35*. Mine was pinging at part throttle, moderate and even light loads once the engine was heat soaked from several hours of highway driving. I tried reducing how quickly vacuum advance came in but that it didnt fully address the problem. That's how I narrowed it down to being too much mechanical advance betwen 2000 and 2800 rpm rather than too much total or too much vacuum advance.