Engine shakes BADLY!!

So I found that the part number is a oem 340 damper....that I believe is neutral/internal balanced.
If that's correct this balancer should work?right?....I have no idea where else to look
128668? OEM PN would be 7 digits.... mid'72 or earlier OEM 340 damper would be internally balanced. Sounds right but not 100% sure of that PN.