It's a 360. I built it.... .030 over new pistons bearings etc. I've never had a problem with stock motors being out of balance after a rebuild. The factory slapped them together and sent 'em and manufacturing variances were way out compared to modern piston technology. Sure, you could be right it... the motor could be out of balance, but my suspicions lean toward this converter at the moment.
Good point on the balancer, and I do have the correct harmonic balancer on the motor. I knew about that, just wasn't sure about the torque converter.