1990 Fox With 1980 302 Accessory Bracket?

That is exactly when an imbalance kicks in when both the harmonic balancer and the rear plate are off balance. But when both are off, it continues to shake like heck as the RPM's rise. (A know it all Chevy guy installed an E7 block in my 79 and refused to use the new balancer and flywheel.) When one is right and one is wrong, who knows how it will shake. My question now is, what year block and what rotating assembly do you have in that block? If it is not right, it will shake itself apart.