Does the ESC resmble this: http://www.hobbyking.com/hobbyking/s...USHED_ESC.html
The 3 small wires (red, white, black) go to thr RX. Two bigger wires are battery.
If the motor is okay, you could get away with this, assuming you have a separate RX somewhere in the model. When you are ready to go upgrading, the brushless system is way more efficient and better power per size, so it will be a treat when you go to it