The flywheel answers you have gotten are correct.
I have read that the way to do a flywheel
swap and retain the
original balance mating to the crank is to bolt
the new flywheel to the old ,back to back,
[ that puts them 180 out ], and balance them as a unit. Then, when you unbolt them , the
new one will be balanced [ actually-unbalanced] the same as the old.
Now when it is bolted back to the original crank, everything is balanced.
I have never done a flex plate /flywheel like this, but something to think over.
I will do some further checking.