The best reverse setup was by kyosho, called the QRC

QRC (Quick Reverse Clutch)Unit
This simple construction consisting of five gears, shafts and a clutch arm, allows any two channel, two servo, radio operated, engine powered car to drive forward and backward just like the full-scale counterparts. Engine power is transmitted via the spur gear to the forward and reverse drive gears. These rotate the clutch gears. Depending on your throttle inputs, the throttle servo-controlled clutch arm engages either into the forward or reverse clutch gear. The clutch gears transmit the power further on to the front and rear wheels via an efficient shaft drive system. The system is unique and quite reliable and operates quickly ensure rapid direction changing.