You are welcome. Just figure out two signal lines of inputs to those bridges, "cut-in" with arduino and you would be able to take full control of the car.
Some thoughts:
- turn on/off leds representing right/left turning signals;
- -//- front/rear lights;
- "beep" horn;
- add voice module, which would play "yes, sir!" or "no, sir" whenever radio receiver outputs some signals.