Balancing doesn't "have" to be done, and race builders also alter the balance to allow for some positive benefits by overbalancing. It's actually done with bob weights on the journals, with harmonic, flywheel, and clutch installed - and a fudge factor thrown in for the
oil that might be on the rods, pistons, etc. Which means it's an approximate guess even in the most stringent shops - and they play with it.
Internally balanced, just get a matching harmonic and flywheel, call it done. The clutch, etc is always neutral. About all the harmonic and flywheel do is add the oz per factory standards because they left it off the crank. Get ones without, its already done. Exactly why racers use internal balance, so they don't have that problem when reassembling stuff. They bolt on whatever neutral parts they need, engine in car, car on track, done.