The 617 balance can be done piece meal in a shop, spinning everything up at the factory is likely more cost effective when you are building thousands of engines. The pistons, rings, rods and bearings are weighed then bob weights clamped to crankshaft rod journals to simulate these parts. This assembly is then spun up on a balancer. Some engine builders purposely under / overbalance to counteract internal forces, tune to RPM ranges making balancing somewhat of a black art.

For internal balance cranks, no other parts are needed. For external, the vibration damper and flywheel need to be installed.