Whether you have an internally or exterally balanced engine is irrelevant. Having your engine dynamically balanced requires all the parts of the reciprocating engine. This includes the crankshaft, flywheel or flex plate, harmonic balancer, pistons, rods, bearings, and rings, cam drive gear on the crank, and key that locates the cam drive gear. Some even go so far as to include the torque converter if its automatic, or clutch disc and pressure plate, if standard shift.
Dittos what was said in the previous post about checking valve clearances with the pistons first. Having pistons flycut does change the weight.