I have converted a couple of planes to taildraggers, and it usually doesn't change the CG all that much. The gear doesn't weigh all that much compared to the motor and radio. Plus it is close to the CG so moving the weight of the gear doesn't do much since you are removing the weight(and drag) of the nose gear. The wheels need to be a little in front of the leading edge. And they need to be toed in some to make it track straight on takeoff. Things can get exciting with toe-out in them. Makes rudder input get overcorrected.