Hello Keeto,
I used 3mm LEDs, fitted a big capacitor inside to keep them from blinking with the throttle on/off. Its an SCX version with in-line motor so enough space for the LEDs. You chose the more difficult Hornby sidewinder...
I'm really a rally fan, I did the Aston for a friend who is a big Aston fan. I also wanted to back-light the door numbers but ran out of time.