You have a relay and a solenoid that must be addressed. Relay would be easy to change to a 12V unit. Solenoid is going to be an issue that can be dealt with by resistors. Not an expert here but someone with knowledge can compute the resistor value based upon the amp draw and ohms resistance within the solenoid. Contacts in the governor and the carb switch (kickdown switch) should not be an issue. Here is a link that should help you understand the electrical needs you have.
http://www.imperialclub.com/Repair/Lit/Master/012B/
http://www.imperialclub.com/Repair/Lit/Master/012B/