With a Delco "12 volt" coil and a ceramic resistor for GM vehicles from the mid-1950's to the early 70's, you should see about 9 volts at the coil + terminal with the ignition on, points closed, and engine stopped. Since charging system voltage against a fully charged battery should be 14-something, voltage at the coil will be slightly higher, maybe 10.5 or so while running. Either way, the resistor should drop about 1/4 of the applied voltage. It sounds like you've been running too much primary resistance, resulting in low firing voltage to the plugs on acceleration. Be sure you have some type of resistor bypass system in place to supply full battery voltage to the coil during starting.
Jerry
