The transistorized ignition will need to be disconnected as the 123 has its own transistorized control built in. The coil must have resistance of at least 1.0 ohms. The Bosch “Red” coil (0 221 119 030) is a good replacement. Be sure to bypass the ballast resistors. You can leave them in place for visual asthetics. Just move the wire going to the coil over to the input side of the balast resistor. If you have the secondary ballast resistor for increased cranking voltage, it can be disconnected.