By way of elaboration of the explanation. I believe that most flywheels are neutrally balanced but some (in my case one out of four) will not balance neutrally because the crank will not. In that case the flywheel is used to make a crank/ flywheel unit neutral. To be sure mark both your flywheels to the cranks they come from and have them both checked. If the flywheel from the engine you want to use is not neutral then the new flywheel must be balanced to match that flywheel and bolted to the crank in the same place.

You don't want to guess on this because if you happen to get one that is not neutral and have a mismatch it will shake your teeth loose. It is not worth the risk since the only solution is to remove it all and do it right the second time.

Good luck, most of them are neutral.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.