I read the whole thread and didn't notice it was old, until pointed out
While reading, I didn't see much focus on the spring loaded clutch disk hub. When I was a mechanic, in general, the #1 cause of chatter was worn spring seats and collapsed or broken springs. You need to check the springs for looseness, even in new clutch discs, especially rebuilt's. They shouldn't be have any movement. As a young street racer, I collapsed and broke, a few hub springs, too
It's always prudent to indicate the flywheel if you've had it off. You should check the fit of the pilot bearing and indicating the trans pilot and mounting face, is good if you have the ability but shouldn't cause chatter. Misalignment will cause fast front bearing and pocket bearing wear.