I too have measured several "6", "12", and "24" volt coils and all had the same primary resistance. Both the 12V and 24V systems used 1.5ohm ballast resistors. I didn't quantify the outputs but there was no noticable difference in the maximum length of the spark/voltage between stock and hi po coils when triggered by points. In other words, a stock coil is fine for points ignitions. The important parameter is the current. Too little won't saturate the coil and give you full output; too much overheats the coil, burns out the points, and provides no additional energy. The main benefit to going to higher voltages is that the coil saturates quicker. The was needed to go to the higher rpm and 8 cylinder engines which had less dwell time.
