A easier method,, though it should have been done when upgraded is to go with modular TMCC upgrade. You could have used a Engine Mother board with R2LC and an ACDR for the Pre War Motor. You can let AC Track Power directly into the ACDR which is just a H Bridge Triac circuit for controlling the motor.
You could have than used a small device to take the High AC input and regulate it down to a constant 16-18VAC and send this to the R2lC mother board. Since the ACDR and the Mother Board only have a PWM DC Connection between them this would keep Voltage in the right range for the TMCC components. The ACDR can handle a Higher AC Voltage. G
