IMO, the only way to balance a crank is dynamically. Which is expensive, and few shops are equipped to do a proper job. I worked on a hot rod CB750 once that had some uncomfortable vibes for the owner, so I sent the entire rotating assembly (crank, flywheel, rods, pistons, etc.) out to Falicon and they did a proper dynamic balance to ensure it was as perfect as it could be. When we fired everything back up, you wouldn't even disturb a glass of water on the tank more than some ripples throughout the whole RPM range. The owner said the bike was better than it ever was even new!
I considered a dynamic balance on my XS bobber (still am actually) project, but it's currently out of the budget.