351C Flexplate balance weight?

[Dana45]

I have a '69 fastback with a '73 351c 4 bolt main with a FMX transmission that was just rebuild and has a new harmonic balancer and a new flexplate but the car has some vibration when you raise the rpm's and it feels out of balance. I suspect the flexplate and would like to know if there are different weights for 351c engines and what is the correct one.