i purchaced this car in pieces in 2007 with the motor half built. i finished putting it together and it runs fine.It does have a very small vibration. On the engine reciept it says balance assembly $215.Now im having transmission problems and ordered a new pump and torque converter from ck performance. i also want a new flexplate but i dont know whether to get a internal or external balanced one. It has a stock crank. Any advice???