My swap ('83 Getrag 4spd. behind a '85 OM617) but have yet to fire it up. Nothing was marked on either engine so my assumption is that all were neutral balanced.

Having worked for over 30 years in dynamometer testing I have a fall back. The finished product can be taken to an industrial balance specialist and they can balance the assembly in place. We did it frequently. They'll hook up several accelerometers that read in all planes and determine any imbalance, then add or subtract weight as needed to resolve any issues found. From there on you can mark any pieces you might have to remove (say, to renew the clutch) and maintain balance for the life of the car. Most cities of any size will have a balance specialist and most don't charge a ton of money for this. Our guy came to us but you can work out those details with the vendor.

Dan