Violent Take-Off Shudder

I seem to recall pulling the gearbox back, and unbolting the pressure plate one bolt at a tine, with the bell still bolted up, and dropping the disc out the bottom..or was I dreaming? I cant remember why I would have done it that way but yes, small block 4 speed I can have out in an hour...or should I say "in my youngrer days...":) My issue ended up being a bad pressure plate, one of the balancing weights flew off at some point or it was defective when new. But I could run it a 2000rpm in neutral and it would shake and vibrate terribly. The point is to the OP "you will get good at pulling the transmission quickly" chasing down this one...