Engine/drivetrain vibration?

My thoughts....
First...REPLACE THAT BALANCER. Its a good rule of thumb to replace the balancer when doing a rebuild.....the rubber could have deteriorated and the outer ring slipped on the inner thus making it so timing is off and balance is off.
Secondly, take the driveshaft i to make sure its balanced correctly.
Thirdly, defintely get the B&M flexplate for your application.

Eliminate the variables BEFORE you pull the engine.