On summits web site you can select coils by primary resistance. For example the Mallory 30451 "E" core coil has a primary resistance of 1.4 Ohms. I think that is close to combination of a stock coil primary resistance (around 0.7 Ohm) plus the ballast resistor (around 0.85 Ohm.)
Really, the worst case (hardest on the coil and ignition box) is with the ignition on, but the engine not running. With no distributor signal to the ignition box, the output transistor is on, grounding the coil so this is when the maximum current will flow through the coil and ignition box, with the current be limited (mostly) by the coils primary resistance. When the engine is running, the ignition box is switching on and off, and the ignition coils inductance will also limit the amount of current flowing through the coil/ignition box.