It is not necessary to balance a rear pod. There was a whole discussion about this on a thread here that I can't find now. Lots of people gave lots of theories... until Mike Blackstock wrote that he had tried this and his car handled better with the standard set-up than with a balanced pod! The conversation then stopped...

As the weight of the whole pod and motor sits on three points it will distribute the weight pretty much evenly across the tyres and the centre pivot. In any event, all the weight goes to the chassis goes through the centre pivot into the chassis, and so any uneveness in the balance will only affect rear tyres, not chassis balance. If the car takes off straight, and pulls evenly out of left and right turns then the motor torque is getting evenly to the tyres and all is well. Modern cars are very good on pod balance as standard, so don't worry. HTH