Well you might be right but Im not going to do that. I don't accept that is necessary yet either. My Buick book does say production engines are balanced with the flywheel. The engine is smooth running now and changing to a heavier flywheel from a flex-plate shouldn't affect balance if weighted the same. Should get the same level of smoothness possibly alittle more as the heavier flywheel should make smoother idle but accelerate slower. Ive never heard of engines requiring rebalancing when changing flywheel weight. Im building a Harley sport 1100+ engine now as well, they just guestimated the balance on my 86 engine and then mass-produced balance by casting voids in the wheels(crank) that are identical, I did hand balance that as I changed pinion shaft and desired a smoother than factory engine .. they used to hand select the 4 gear drive cams to mate together from several different sizes for fit as well, I don't believe gm went that far on an engine for a passenger car, that would make a nightmare for replacement parts. They probaby just guesstimated a value and all flywheels are set at for a given application. I could be wrong, maybe thats the nightmare Im in right now. No mechanic Ive ever spoken to acknowledges an issue concerning that tho. The machine shop does shows a 200$ fee for flywheel balancing.