Whether you choose to listen for the pinging or watch the vacuum shouldn't deter anyone from using a timing light. As Jim and others said, you use the light to set the starting point. From that point, you use the light and increase it by two degrees. You didn't get what you wanted? You use the light and add two more degrees. Now it's pinging or the vacuum dropped. Use the light and drop it one degree. If this makes you happy, you now have your new timing mark.
You had started at, say four degrees and after putzing around you added three more degrees. The next time you need to set the timing, you set it at seven degrees and be done with it.
I have a digital timing light with the dial-back and a tach. The tach in your old dwell-tach meter may not work with electronic ignition. Mine would not work with the HEI so the timing light tach, takes care of that.
