Need help with vibration

This is frustrating. Finally got engine running and now it has a vibration. Here is what I have.

1972 Dodge Dart original 318/904. Now has a 1974 motorhome 360 with 40k miles. Bottom end looked great when changed oil pan.
Added comp cam XE268H and a set of x heads.
I put in a B&M balance flex plate and neutral balance torque converter from t-flght Pat.
Used the original harmonic balancer but checked top dead center and matched exact.
Broken in cam well. Seemed smooth under the hood at break-in never sat in car.
Now from in the car has a bad vibe starting at about 1200 rpm and up. Vibration drops off as rpms are falling. Can't find anything rubbing or touching.
Any ideas?