Fyi...
I saw a link to a Mopar reseller that offers a Rebuilt balancer.
Remanufactured harmonic balancer for 1967-69 Plymouth Barracuda - Valiant and Dodge Dart with 273/318/340 engine
You send them your Balancer and they rebuild it.
Pricy but if they do a rubber replacement that is OEM quality and surface the sealing surface it might be worth it.