yah you have to change the motor to 4mm plugs. or you can change the mm to 3.5 but i would just change the motor.

as for gearing what i did was stay at stock and run it and then see my temps and go from there. if the temps are good and you like the power you have then keep it where it is. but if you want more top end power then lower your spur and up your pinion. if you want more bottom then up your spur and lower your pinion a little bit.