Need help with vibration in 67 mustang

[mustangII460]

Pre 1980 motors had a 28.2 ounce flex plate and harmonic balancer to match.

Post 1980 have 50 ounce flex plate.

When you look at a 50 ouncer plate,the weight is about 3/4 around the plate.

The 50 harmonic balancer weight covers a litle more than half,around the balancer.

Rule of thumb, it looks like the 50 oncer has twice the mass as a 28.2 ouncer.

Not putting on the right balance will kill your rear main bearings or worse, if your lucky.

Alot of people swap in a AOD but bring the heavy plate too. Thats fine if you rebalance the plate to 28.2 ounces. That is if you have a older motor.