383 harmonic damper

383 cast crank ? That seems odd. I thought all 383's were forged cranks. Sounds like this is a 383 with a 400 crank in it ? Or maybe its a 400 ? If you have the old balancer you could reuse it by having it rebuilt. Take a look in hemmings there are outfits that do this. The other thing to check is the parts houses, somebody probably is producing the correct part in a performance version. A 360 flex plate and or damper wont work, the snout is too long, not to mention the balance wont be right. If the motor is apart why not get a forged crank and do it "right" , with a neutral balance damper and flex plate. Make sure to have the whole mess balanced in any event.