If it's a medium sized indoor clay track, I would say 18/81. That's what I would run in my BJ4WE which is basically the exact same car. Any larger gearing you run the risk of getting the motor soo hot that it will come unsoldered. If it is the aluminum endbell checkpoint then it's not so much of a problem, but plastic, be careful with gearing.
Don't sweat the petty things...........Pet the sweaty things!!