Originally Posted by TomJ

The point is, balanced to what? If you don't have the rotating/reciprocating assy out of the engine (crank, rods, pistons, flywheel, harm balancer, etc.) then you can't just take a flywheel to a balance shop and say "balance it". They need something to balance it TO. If we were dealing with an internally balanced engine, then yes, they could just zero balance it (no offweight balance), but these are externally balanced so they need to know how much counterweight to add to make up for the same amount of "off-balance" that the original flexplate has. That's why the caveat to mark the crank and flexplate BEFORE they are separated, so you can have a shop induce the same "off-balance" at the same place relative to the crank and install the same way.