[rotorwrench]

They generally just drill into the counterweights to remove weight or add weight depending on the imbalance characteristics. We had a discussion on here before about cranks that had more metal loss than expected when the gang of shafts were separated at the foundry after casting. There have also been some discussions about balancing.

Prepping one for racing applications is a lot more involved than just balancing one.

Ford would grind off lumps and smooth out flashing before machining the shafts for front & rear shafting & flange, oil flow ports, and bearing journals. I don't know what there inspection procedures were but they likely performed some NDT inspection to weed out any that were obviously not going to pass QC. The clean out plugs would likely have been the last thing installed. Balancing would have been performed prior to sending them on to the assembly line. Sometimes the funky looking stuff lasts longer than the nice looking stuff.