Ok, so I should be able to take the original and a replacement damper/balancer to a machine shop and have them matched without needing to pull the crankshaft and flywheel. Good.

Now a related question... as mentioned, the pins on the original balancer are missing and the locating holes are a bit wallered out. I have no way of knowing if it spun on the crank at some point, but it's obviously suspect. I assume an out-of-balance crankshaft could damage the seals over time, but if they're okay should I worry about anything internal? Bearings? Play?